diff --git a/CHANGELOG.md b/CHANGELOG.md
index c946fbbf104..cbc3b5290b9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 * perf(sdk-trace-base): use Uint8Array for browser RandomIdGenerator [#6209](https://github.com/open-telemetry/opentelemetry-js/pull/6209) @overbalance
 * test(sdk-trace-base): remove obsolete TypeScript and platform workarounds [#6327](https://github.com/open-telemetry/opentelemetry-js/pull/6327) @overbalance
 * fix(example-web): update Docker config and deps for collector [#6342](https://github.com/open-telemetry/opentelemetry-js/pull/6342) @overbalance
+* perf(sdk-trace-base): optimize setAttribute performance [#6283](https://github.com/open-telemetry/opentelemetry-js/pull/6283) @AbhiPrasad
 
 ## 2.5.0
 
diff --git a/packages/opentelemetry-sdk-trace-base/src/Span.ts b/packages/opentelemetry-sdk-trace-base/src/Span.ts
index 508557f6a34..c9b1cd9cabe 100644
--- a/packages/opentelemetry-sdk-trace-base/src/Span.ts
+++ b/packages/opentelemetry-sdk-trace-base/src/Span.ts
@@ -93,6 +93,7 @@ export class SpanImpl implements Span {
   private _droppedAttributesCount = 0;
   private _droppedEventsCount: number = 0;
   private _droppedLinksCount: number = 0;
+  private _attributesCount: number = 0;
 
   name: string;
   status: SpanStatus = {
@@ -157,16 +158,24 @@ export class SpanImpl implements Span {
     }
 
     const { attributeCountLimit } = this._spanLimits;
+    const isNewKey = !Object.prototype.hasOwnProperty.call(
+      this.attributes,
+      key
+    );
 
     if (
       attributeCountLimit !== undefined &&
-      Object.keys(this.attributes).length >= attributeCountLimit &&
-      !Object.prototype.hasOwnProperty.call(this.attributes, key)
+      this._attributesCount >= attributeCountLimit &&
+      isNewKey
     ) {
       this._droppedAttributesCount++;
       return this;
     }
+
     this.attributes[key] = this._truncateToSize(value);
+    if (isNewKey) {
+      this._attributesCount++;
+    }
     return this;
   }
 
diff --git a/packages/opentelemetry-sdk-trace-base/test/performance/benchmark/setAttributes.js b/packages/opentelemetry-sdk-trace-base/test/performance/benchmark/setAttributes.js
new file mode 100644
index 00000000000..ef0d96c4bc1
--- /dev/null
+++ b/packages/opentelemetry-sdk-trace-base/test/performance/benchmark/setAttributes.js
@@ -0,0 +1,99 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const Benchmark = require('benchmark');
+const { BasicTracerProvider } = require('../../../build/src');
+
+const tracerProvider = new BasicTracerProvider();
+const tracer = tracerProvider.getTracer('test');
+
+const suite = new Benchmark.Suite('setAttribute performance');
+
+suite.on('cycle', event => {
+  console.log(String(event.target));
+});
+
+// Generate attribute keys for different test sizes
+function generateAttributeKeys(count) {
+  const keys = [];
+  for (let i = 0; i < count; i++) {
+    keys.push(`attribute_key_${i.toString().padStart(4, '0')}`);
+  }
+  return keys;
+}
+
+const keys10 = generateAttributeKeys(10);
+const keys50 = generateAttributeKeys(50);
+const keys100 = generateAttributeKeys(100);
+const keys128 = generateAttributeKeys(128);
+
+// Test with 10 attributes
+suite.add('setAttribute (10 attributes)', function () {
+  const span = tracer.startSpan('span');
+  for (let i = 0; i < keys10.length; i++) {
+    span.setAttribute(keys10[i], 'test_value');
+  }
+  span.end();
+});
+
+// Test with 50 attributes
+suite.add('setAttribute (50 attributes)', function () {
+  const span = tracer.startSpan('span');
+  for (let i = 0; i < keys50.length; i++) {
+    span.setAttribute(keys50[i], 'test_value');
+  }
+  span.end();
+});
+
+// Test with 100 attributes
+suite.add('setAttribute (100 attributes)', function () {
+  const span = tracer.startSpan('span');
+  for (let i = 0; i < keys100.length; i++) {
+    span.setAttribute(keys100[i], 'test_value');
+  }
+  span.end();
+});
+
+// Test with 128 attributes (default limit)
+suite.add('setAttribute (128 attributes - at limit)', function () {
+  const span = tracer.startSpan('span');
+  for (let i = 0; i < keys128.length; i++) {
+    span.setAttribute(keys128[i], 'test_value');
+  }
+  span.end();
+});
+
+// Test setAttribute with overwriting existing keys (no Object.keys growth)
+suite.add('setAttribute (100 overwrites of same key)', function () {
+  const span = tracer.startSpan('span');
+  for (let i = 0; i < 100; i++) {
+    span.setAttribute('same_key', 'test_value_' + i);
+  }
+  span.end();
+});
+
+// Test setAttributes in bulk vs individual setAttribute
+suite.add('setAttributes bulk (100 attributes)', function () {
+  const span = tracer.startSpan('span');
+  const attrs = {};
+  for (let i = 0; i < 100; i++) {
+    attrs[keys100[i]] = 'test_value';
+  }
+  span.setAttributes(attrs);
+  span.end();
+});
+
+suite.run({ async: false });