Disclosed is a method of transmitting a media independent handover (MIH) protocol message in a wireless access system. A method for a mobile node to transmit an MIH message in a wireless access system includes receiving a primitive including prescribed information from a first entity, generating the MIH message by mapping a transport address to the primitive, and transmitting the MIH message to one or more network nodes. According to the present invention, transmission defects of the message are effectively reduced by accurately mapping an MIHF ID and a transport address.