An authentication method and apparatus in a communication system are provided. In a method for authenticating a first node at a second authentication server in a communication system comprising the first node registered to a first authentication server and a second node registered to the second authentication server, an authentication request message requesting authentication of the first node is received from the second node, the authentication request message is transmitted to the first authentication server, and upon receipt of an authentication success message indicating successful authentication of the first node from the first authentication server, the authentication success message is transmitted to the second node.