The present invention relates to an authentication method for wireless distribution system including at least one base station providing access service to mobile stations in a coverage of the base station. In the authentication method, an unregistered base station receives an authentication request from a mobile station, multicast an identity request for identifying the mobile station over the wireless distribution system, receives identity responses from at least one base station in response to the identity request, and performs authentication of the mobile station on the basis of the identity responses. The distributed authentication method of the present invention is performed without AAA server, when a new base station is installed or isolated base stations are joined, such that it is possible to extend the network in an easy manner without degradation of the security degree and additional labor burden of the operator.