A method of transmitting a neighbor discovery protocol (NDP) message in an IEEE 802.16/Wibro network is provided. The method of transmitting an NDP message in a sub-network formed with access routers and a plurality of base stations connected to the access router through separate interfaces includes: a first base station transmitting a first NDP message received from a first terminal, to the access router; and the access router transmitting the first NDP message to the remaining base stations excluding the first base station. According to the method, a method of processing an NDP message in an environment having multiple base stations which cannot be considered under a conventional environment using a multicast connection ID (CID) can be improved, and problems that can occur when a IPv6 is introduced in an IEEE 802.16/Wibro network can be solved.