diff --git a/src/client/factory.ts b/src/client/factory.ts
index 70943aec..61b5f736 100644
--- a/src/client/factory.ts
+++ b/src/client/factory.ts
@@ -75,7 +75,7 @@ export const ClientFactoryOptions = {
 };
 
 export class ClientFactory {
-  private readonly transportsByName: Map<string, TransportFactory>;
+  private readonly transportsByName: CaseInsensitiveMap<TransportFactory>;
   private readonly agentCardResolver: AgentCardResolver;
 
   constructor(public readonly options: ClientFactoryOptions = ClientFactoryOptions.default) {
@@ -84,8 +84,7 @@ export class ClientFactory {
     }
     this.transportsByName = transportsByName(options.transports);
     for (const transport of options.preferredTransports ?? []) {
-      const factory = this.options.transports.find((t) => t.protocolName === transport);
-      if (!factory) {
+      if (!this.transportsByName.has(transport)) {
         throw new Error(
           `Unknown preferred transport: ${transport}, available transports: ${[...this.transportsByName.keys()].join()}`
         );
@@ -100,7 +99,7 @@ export class ClientFactory {
   async createFromAgentCard(agentCard: AgentCard): Promise<Client> {
     const agentCardPreferred = agentCard.preferredTransport ?? JsonRpcTransportFactory.name;
     const additionalInterfaces = agentCard.additionalInterfaces ?? [];
-    const urlsPerAgentTransports = new Map<string, string>([
+    const urlsPerAgentTransports = new CaseInsensitiveMap<string>([
       [agentCardPreferred, agentCard.url],
       ...additionalInterfaces.map<[string, string]>((i) => [i.transport, i.url]),
     ]);
@@ -165,8 +164,8 @@ function mergeTransports(
 
 function transportsByName(
   transports: ReadonlyArray<TransportFactory> | undefined
-): Map<string, TransportFactory> {
-  const result = new Map<string, TransportFactory>();
+): CaseInsensitiveMap<TransportFactory> {
+  const result = new CaseInsensitiveMap<TransportFactory>();
   if (!transports) {
     return result;
   }
@@ -189,3 +188,29 @@ function mergeArrays<T>(
 
   return [...(a1 ?? []), ...(a2 ?? [])];
 }
+
+/**
+ * A Map that normalizes string keys to uppercase for case-insensitive lookups.
+ * This prevents errors from inconsistent casing in protocol names.
+ */
+class CaseInsensitiveMap<T> extends Map<string, T> {
+  private normalizeKey(key: string): string {
+    return key.toUpperCase();
+  }
+
+  override set(key: string, value: T): this {
+    return super.set(this.normalizeKey(key), value);
+  }
+
+  override get(key: string): T | undefined {
+    return super.get(this.normalizeKey(key));
+  }
+
+  override has(key: string): boolean {
+    return super.has(this.normalizeKey(key));
+  }
+
+  override delete(key: string): boolean {
+    return super.delete(this.normalizeKey(key));
+  }
+}
diff --git a/test/client/factory.spec.ts b/test/client/factory.spec.ts
index b4fa52b1..96f76872 100644
--- a/test/client/factory.spec.ts
+++ b/test/client/factory.spec.ts
@@ -50,7 +50,7 @@ describe('ClientFactory', () => {
         preferredTransports: ['UnknownTransport'],
       };
       expect(() => new ClientFactory(options)).to.throw(
-        'Unknown preferred transport: UnknownTransport, available transports: Transport1'
+        'Unknown preferred transport: UnknownTransport, available transports: TRANSPORT1'
       );
     });
 
@@ -71,6 +71,30 @@ describe('ClientFactory', () => {
 
       expect(factory.options).to.equal(options);
     });
+
+    it('should accept preferred transport with different case', () => {
+      const options: ClientFactoryOptions = {
+        transports: [mockTransportFactory1],
+        preferredTransports: ['transport1'], // lowercase, but Transport1 is registered
+      };
+
+      // Should not throw
+      const factory = new ClientFactory(options);
+
+      expect(factory.options).to.equal(options);
+    });
+
+    it('should detect duplicate transports with different case as duplicates', () => {
+      const transport1Lower = {
+        protocolName: 'transport1', // lowercase
+        create: vi.fn(),
+      };
+      const options: ClientFactoryOptions = {
+        transports: [mockTransportFactory1, transport1Lower], // Transport1 and transport1
+      };
+
+      expect(() => new ClientFactory(options)).to.throw('Duplicate protocol name: transport1');
+    });
   });
 
   describe('createClient', () => {
@@ -163,6 +187,46 @@ describe('ClientFactory', () => {
       expect(client.config).to.equal(clientConfig);
     });
 
+    it('should match transport with case-insensitive protocol name', async () => {
+      // Transport factory uses "Transport1" but agent card uses "transport1" (lowercase)
+      agentCard.preferredTransport = 'transport1';
+      const factory = new ClientFactory({ transports: [mockTransportFactory1] });
+
+      const client = await factory.createFromAgentCard(agentCard);
+
+      expect(client).to.be.instanceOf(Client);
+      expect(mockTransportFactory1.create).toHaveBeenCalledExactlyOnceWith(
+        'http://transport1.com',
+        agentCard
+      );
+    });
+
+    it('should match HTTP+JSON transport regardless of case', async () => {
+      const httpJsonFactory = {
+        protocolName: 'HTTP+JSON',
+        create: vi.fn().mockResolvedValue(mockTransport),
+      };
+      agentCard.preferredTransport = 'http+json'; // lowercase
+      const factory = new ClientFactory({ transports: [httpJsonFactory] });
+
+      await factory.createFromAgentCard(agentCard);
+
+      expect(httpJsonFactory.create).toHaveBeenCalledTimes(1);
+    });
+
+    it('should match JSONRPC transport regardless of case', async () => {
+      const jsonRpcFactory = {
+        protocolName: 'JSONRPC',
+        create: vi.fn().mockResolvedValue(mockTransport),
+      };
+      agentCard.preferredTransport = 'JsonRpc'; // mixed case
+      const factory = new ClientFactory({ transports: [jsonRpcFactory] });
+
+      await factory.createFromAgentCard(agentCard);
+
+      expect(jsonRpcFactory.create).toHaveBeenCalledTimes(1);
+    });
+
     it('should use card resolver with default path', async () => {
       const cardResolver = {
         resolve: vi.fn().mockResolvedValue(agentCard),