diff --git a/crates/loro-internal/src/container/richtext/richtext_state.rs b/crates/loro-internal/src/container/richtext/richtext_state.rs
index db9f02f01..1bbf24a30 100644
--- a/crates/loro-internal/src/container/richtext/richtext_state.rs
+++ b/crates/loro-internal/src/container/richtext/richtext_state.rs
@@ -1477,6 +1477,23 @@ impl RichtextState {
         result
     }
 
+    /// Whether every position in the entity range already resolves `key` to
+    /// `value`, in which case a mark with that key and value can be skipped.
+    pub(crate) fn range_has_style_key_value(
+        &mut self,
+        range: Range<usize>,
+        key: &str,
+        value: &LoroValue,
+    ) -> bool {
+        self.check_cache();
+        let result = match self.style_ranges.as_ref() {
+            Some(s) => s.range_has_key_value(range, key, value),
+            None => false,
+        };
+        self.check_cache();
+        result
+    }
+
     /// Return the entity range and text styles at the given range.
     /// If in the target range the leaves are not in the same span, the returned styles would be None
     pub(crate) fn get_entity_range_and_text_styles_at_range(
diff --git a/crates/loro-internal/src/container/richtext/style_range_map.rs b/crates/loro-internal/src/container/richtext/style_range_map.rs
index f7487d4db..350fae0ed 100644
--- a/crates/loro-internal/src/container/richtext/style_range_map.rs
+++ b/crates/loro-internal/src/container/richtext/style_range_map.rs
@@ -219,6 +219,48 @@ impl StyleRangeMap {
         false
     }
 
+    /// Whether every position in the range already resolves `key` to `value`.
+    ///
+    /// Unlike [`Self::get_styles_of_range`], this works when the range spans
+    /// multiple style ranges, so callers can skip marks that would not change
+    /// anything (each redundant mark op leaves a pair of style anchors in the
+    /// state forever).
+    pub(crate) fn range_has_key_value(
+        &self,
+        range: Range<usize>,
+        key: &str,
+        value: &loro_common::LoroValue,
+    ) -> bool {
+        if range.is_empty() || !self.has_style {
+            return false;
+        }
+
+        let mut query = self.tree.query::<LengthFinder>(&range.start).unwrap();
+        let mut pos = range.start;
+        loop {
+            let elem = self.tree.get_elem(query.cursor.leaf).unwrap();
+            let remaining_in_elem = elem.len - query.cursor.offset;
+            if remaining_in_elem > 0 && !elem.styles.has_key_value(key, value) {
+                return false;
+            }
+
+            let next_pos = pos + remaining_in_elem;
+            if next_pos >= range.end {
+                break;
+            }
+
+            match self.tree.next_elem(query.cursor) {
+                Some(next_cursor) => {
+                    pos = next_pos;
+                    query.cursor = next_cursor;
+                }
+                None => break,
+            }
+        }
+
+        true
+    }
+
     /// Insert entities at `pos` with length of `len`
     ///
     /// # Internal
diff --git a/crates/loro-internal/src/handler.rs b/crates/loro-internal/src/handler.rs
index 001a36483..4ba41fea7 100644
--- a/crates/loro-internal/src/handler.rs
+++ b/crates/loro-internal/src/handler.rs
@@ -2340,10 +2340,16 @@ impl TextHandler {
         }
         let (entity_range, styles) =
             state.get_entity_range_and_text_styles_at_range(start..end, pos_type);
-        if let Some(styles) = styles {
-            if styles.has_key_value(&key, value) {
-                return Ok(());
-            }
+        // `styles` is None when the range spans multiple style ranges; fall
+        // back to scanning them so redundant marks are still skipped instead
+        // of accumulating style anchors.
+        let already_applied = styles.map(|styles| styles.has_key_value(&key, value));
+        let already_applied = match already_applied {
+            Some(applied) => applied,
+            None => state.range_has_style_key_value(entity_range.clone(), &key, value),
+        };
+        if already_applied {
+            return Ok(());
         }
 
         let has_target_style =
@@ -2436,10 +2442,20 @@ impl TextHandler {
                 let (entity_range, styles) =
                     state.get_entity_range_and_styles_at_range(start..end, pos_type);
 
-                let skip = styles
+                // `styles` is None when the range spans multiple style
+                // ranges; fall back to scanning them so redundant marks are
+                // still skipped instead of accumulating style anchors.
+                let skip = match styles
                     .as_ref()
                     .map(|styles| styles.has_key_value(&key, &value))
-                    .unwrap_or(false);
+                {
+                    Some(skip) => skip,
+                    None => state.has_style_key_value_in_entity_range(
+                        entity_range.clone(),
+                        &key,
+                        &value,
+                    ),
+                };
                 let has_target_style = state.has_style_key_in_entity_range(
                     entity_range.clone(),
                     &StyleKey::Key(key.clone()),
diff --git a/crates/loro-internal/src/state/richtext_state.rs b/crates/loro-internal/src/state/richtext_state.rs
index 0060669fa..61706f856 100644
--- a/crates/loro-internal/src/state/richtext_state.rs
+++ b/crates/loro-internal/src/state/richtext_state.rs
@@ -961,6 +961,17 @@ impl RichtextState {
         self.state.get_mut().range_has_style_key(range, key)
     }
 
+    pub(crate) fn has_style_key_value_in_entity_range(
+        &mut self,
+        range: Range<usize>,
+        key: &str,
+        value: &LoroValue,
+    ) -> bool {
+        self.state
+            .get_mut()
+            .range_has_style_key_value(range, key, value)
+    }
+
     /// Check if the content and style ranges are consistent.
     ///
     /// Panic if inconsistent.
diff --git a/crates/loro-internal/tests/richtext.rs b/crates/loro-internal/tests/richtext.rs
index 553c8e594..5347357d6 100644
--- a/crates/loro-internal/tests/richtext.rs
+++ b/crates/loro-internal/tests/richtext.rs
@@ -361,3 +361,66 @@ fn insert_after_link() {
     doc_a.check_state_diff_calc_consistency_slow();
     doc_b.check_state_diff_calc_consistency_slow();
 }
+
+#[test]
+fn redundant_mark_spanning_style_boundaries_creates_no_ops() {
+    let doc = init("Hello World");
+    mark(&doc, 0..5, Kind::Bold);
+    // This range spans a style boundary, so it genuinely changes 5..11.
+    mark(&doc, 0..11, Kind::Bold);
+    doc.commit_then_renew();
+    let vv = doc.oplog_vv();
+
+    // The whole text is already bold; re-asserting the mark must not record
+    // new ops, even though the range spans multiple style ranges. Every
+    // redundant mark op leaves a pair of style anchors in the container state
+    // forever, permanently slowing down styled reads.
+    mark(&doc, 0..11, Kind::Bold);
+    doc.commit_then_renew();
+    assert_eq!(doc.oplog_vv(), vv);
+    expect_result(
+        &doc,
+        serde_json::json!([
+            {"insert": "Hello World", "attributes": {"bold": true}},
+        ]),
+    );
+}
+
+#[test]
+fn redundant_unmark_spanning_style_boundaries_creates_no_ops() {
+    let doc = init("Hello World");
+    mark(&doc, 0..5, Kind::Bold);
+    mark(&doc, 6..11, Kind::Bold);
+    unmark(&doc, 0..11, Kind::Bold);
+    doc.commit_then_renew();
+    let vv = doc.oplog_vv();
+
+    unmark(&doc, 0..11, Kind::Bold);
+    doc.commit_then_renew();
+    assert_eq!(doc.oplog_vv(), vv);
+    expect_result(
+        &doc,
+        serde_json::json!([
+            {"insert": "Hello World", "attributes": {"bold": false}},
+        ]),
+    );
+}
+
+#[test]
+fn mark_that_changes_part_of_the_range_still_applies() {
+    let doc = init("Hello World");
+    mark(&doc, 0..5, Kind::Bold);
+    doc.commit_then_renew();
+    let vv = doc.oplog_vv();
+
+    // 0..5 is already bold but 5..11 is not, so this must not be skipped.
+    mark(&doc, 0..11, Kind::Bold);
+    doc.commit_then_renew();
+    assert_ne!(doc.oplog_vv(), vv);
+    expect_result(
+        &doc,
+        serde_json::json!([
+            {"insert": "Hello World", "attributes": {"bold": true}},
+        ]),
+    );
+}
diff --git a/crates/loro/tests/perf_redundant_marks.rs b/crates/loro/tests/perf_redundant_marks.rs
new file mode 100644
index 000000000..4bd8434ea
--- /dev/null
+++ b/crates/loro/tests/perf_redundant_marks.rs
@@ -0,0 +1,48 @@
+use loro::LoroDoc;
+use std::time::Instant;
+
+/// Regression guard for style-anchor accumulation from redundant marks.
+///
+/// The skip-redundant-marks check in `mark_with_txn` used to work only when
+/// the marked range fell inside a single style-range leaf, so on any styled
+/// document a caller re-asserting a mark that changes nothing (e.g. an editor
+/// binding syncing mark state) recorded a new op every time. Each of those
+/// ops leaves a pair of style anchors in the container state forever — they
+/// survive snapshots and are never consolidated — and every styled read pays
+/// for all of them, so reads degraded without bound. After the fix redundant
+/// marks are skipped, so read time should stay flat as `n` grows.
+///
+/// Run with:
+/// cargo test -p loro perf_redundant_marks_do_not_degrade_styled_reads -- --ignored --nocapture
+#[test]
+#[ignore]
+fn perf_redundant_marks_do_not_degrade_styled_reads() {
+    fn bench(n: usize) -> std::time::Duration {
+        let doc = LoroDoc::new();
+        let text = doc.get_text("text");
+        text.insert(0, &"x".repeat(724)).unwrap();
+        // Fragment the style ranges so the redundant marks below take the
+        // spans-multiple-leaves path.
+        text.mark(0..100, "bold", true).unwrap();
+        text.mark(0..724, "bold", true).unwrap();
+        for _ in 0..n {
+            text.mark(0..724, "bold", true).unwrap();
+        }
+        doc.commit();
+
+        let start = Instant::now();
+        for _ in 0..100 {
+            std::hint::black_box(text.get_richtext_value());
+        }
+        start.elapsed() / 100
+    }
+
+    let mut prev = 0f64;
+    for &n in &[0usize, 1000, 2000, 4000] {
+        let d = bench(n);
+        let us = d.as_secs_f64() * 1e6;
+        let ratio = if prev > 0.0 { us / prev } else { 0.0 };
+        println!("redundant_marks={n:>5}  read={us:>9.2} us  x_vs_prev={ratio:.2}");
+        prev = us;
+    }
+}