Methods and apparatuses are provided for releasing an internet protocol (IP) address by a packet data network gateway (PGW) in a mobile communication system. The PGW allocates an IP version 4 (IPv4) address and an IP version 6 (IPv6) address to a terminal to establish a packet data network (PDN) connection between the terminal and the PGW. The PGW identifies a PDN type associated with the PDN connection if an event of releasing the IPv4 address has occurred. The PGW transmits, to a serving gateway (SGW), a binding revocation message, including information indicating release of the IPv4 address, with the PDN connection remaining, if the PDN type is IPv4 and IPv6. The PGW receives a binding revocation acknowledge message in response to the binding revocation request message, from the SGW.