diff --git a/lib/utils.ts b/lib/utils.ts
index e65ebc95..d3e29903 100644
--- a/lib/utils.ts
+++ b/lib/utils.ts
@@ -13,17 +13,35 @@ export function ensureJSON<T>(raw: T): T {
   }
 }
 
+function toArrayBuffer(input: Uint8Array | Buffer): ArrayBuffer {
+  if (input.buffer instanceof ArrayBuffer) {
+    return input.buffer.slice(
+      input.byteOffset,
+      input.byteOffset + input.byteLength,
+    );
+  }
+  const arrayBuffer = new ArrayBuffer(input.byteLength);
+  new Uint8Array(arrayBuffer).set(input);
+  return arrayBuffer;
+}
+
 export function createMultipartFormData(
   this: FormData | void,
   formBody: Record<string, any>,
 ): FormData {
   const formData = this instanceof FormData ? this : new FormData();
-  Object.entries(formBody).forEach(([key, value]) => {
-    if (Buffer.isBuffer(value) || value instanceof Uint8Array) {
-      formData.append(key, new Blob([value]));
+  for (const [key, value] of Object.entries(formBody)) {
+    if (value == null) continue;
+
+    if (value instanceof Blob) {
+      formData.append(key, value);
+    } else if (Buffer.isBuffer(value) || value instanceof Uint8Array) {
+      const arrayBuffer = toArrayBuffer(value);
+      formData.append(key, new Blob([arrayBuffer]));
     } else {
       formData.append(key, String(value));
     }
-  });
+  }
+
   return formData;
 }
diff --git a/package-lock.json b/package-lock.json
index 4a211f4a..b8139ad4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9,8 +9,7 @@
       "version": "1.0.0-test",
       "license": "Apache-2.0",
       "dependencies": {
-        "@types/node": "^22.0.0",
-        "axios": "^1.12.0"
+        "@types/node": "^22.0.0"
       },
       "devDependencies": {
         "@types/express": "5.0.3",
@@ -5153,9 +5152,9 @@
       }
     },
     "node_modules/typescript": {
-      "version": "5.8.3",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.8.3.tgz",
-      "integrity": "sha512-p1diW6TqL9L07nNxvRMM7hMMw4c5XOo/1ibL4aAIGmSAt9slTE1Xgw5KWuof2uTOvCg9BY7ZRi+GaF+7sfgPeQ==",
+      "version": "5.9.2",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.2.tgz",
+      "integrity": "sha512-CWBzXQrc/qOkhidw1OzBTQuYRbfyxDXJMVJ1XNwUHGROVmuaeiEm3OslpZ1RV96d7SKKjZKrSJu3+t/xlw3R9A==",
       "dev": true,
       "license": "Apache-2.0",
       "bin": {
diff --git a/test/client.spec.ts b/test/client.spec.ts
index 89dccdf7..6b5b1e5c 100644
--- a/test/client.spec.ts
+++ b/test/client.spec.ts
@@ -1,7 +1,13 @@
 import { readFileSync } from "node:fs";
 import { Buffer } from "node:buffer";
 import { join } from "node:path";
-import { deepEqual, equal, ok, strictEqual } from "node:assert";
+import {
+  deepEqual,
+  deepStrictEqual,
+  equal,
+  ok,
+  strictEqual,
+} from "node:assert";
 import { URL } from "node:url";
 import Client, { OAuth } from "../lib/client.js";
 import * as Types from "../lib/types.js";
@@ -17,6 +23,7 @@ import {
 
 import { describe, it, beforeAll, afterAll, afterEach } from "vitest";
 import { parseForm } from "./helpers/parse-form";
+import { Readable } from "node:stream";
 
 const channelAccessToken = "test_channel_access_token";
 
@@ -994,7 +1001,7 @@ describe("client", () => {
     equal(scope.isDone(), true);
   });
 
-  it("createUploadAudienceGroupByFile", async () => {
+  it("createUploadAudienceGroupByFile with buffer", async () => {
     const filepath = join(__dirname, "/helpers/line-icon.png");
     const buffer = readFileSync(filepath);
 
@@ -1017,20 +1024,23 @@ describe("client", () => {
               .startsWith(`multipart/form-data; boundary=`),
           );
 
-          const blob = await request.blob();
-          const arrayBuffer = await blob.arrayBuffer();
-          const formData = parseForm(arrayBuffer);
-          equal(formData["description"], requestBody.description);
+          const formData = await request.formData();
+          equal(formData.get("description"), requestBody.description);
           equal(
-            formData["isIfaAudience"],
+            formData.get("isIfaAudience"),
             requestBody.isIfaAudience.toString(),
           );
-          equal(formData["uploadDescription"], requestBody.uploadDescription);
           equal(
-            Buffer.from(await (formData["file"] as Blob).arrayBuffer()),
-            requestBody.file.toString(),
+            formData.get("uploadDescription"),
+            requestBody.uploadDescription,
           );
 
+          const filePart = formData.get("file");
+          ok(filePart instanceof Blob);
+          const sent = Buffer.from(await (filePart as Blob).arrayBuffer());
+
+          deepStrictEqual(sent, requestBody.file);
+
           scope.done();
           return HttpResponse.json({});
         },
@@ -1041,6 +1051,57 @@ describe("client", () => {
     equal(scope.isDone(), true);
   });
 
+  it("createUploadAudienceGroupByFile with Readable stream", async () => {
+    const filepath = join(__dirname, "/helpers/line-icon.png");
+    const buffer = readFileSync(filepath);
+
+    const requestBody = {
+      description: "audienceGroupName",
+      isIfaAudience: true,
+      uploadDescription: "uploadDescription",
+      file: Readable.from(buffer),
+    };
+
+    const scope = new MSWResult();
+    server.use(
+      http.post(
+        DATA_API_PREFIX + "/audienceGroup/upload/byFile",
+        async ({ request }) => {
+          checkInterceptionOption(request, interceptionOption);
+          ok(
+            request.headers
+              .get("content-type")
+              .startsWith("multipart/form-data; boundary="),
+          );
+
+          const formData = await request.formData();
+
+          equal(formData.get("description"), requestBody.description);
+          equal(
+            formData.get("isIfaAudience"),
+            requestBody.isIfaAudience.toString(),
+          );
+          equal(
+            formData.get("uploadDescription"),
+            requestBody.uploadDescription,
+          );
+
+          const filePart = formData.get("file");
+          ok(filePart instanceof Blob);
+
+          const sent = Buffer.from(await (filePart as Blob).arrayBuffer());
+          deepStrictEqual(sent, buffer);
+
+          scope.done();
+          return HttpResponse.json({});
+        },
+      ),
+    );
+
+    await client.createUploadAudienceGroupByFile(requestBody as any);
+    equal(scope.isDone(), true);
+  });
+
   it("updateUploadAudienceGroup", async () => {
     const requestBody = {
       audienceGroupId: 4389303728991,