An apparatus and method for providing a packet data service by using a plurality of heterogeneous networks is provided. The apparatus includes: a controller for allocating a representative IP address to the terminal and for binding sub-IP address, which are allocated to the terminal by the heterogeneous wireless networks, to the representative IP address; a copy unit for copying an IP packet received from an IP network according to the number of wireless networks to which the terminal is currently connected; and a converter for performing packet conversion on the copied IP packets by using corresponding sub-IP addresses and for transmitting the converted IP packets to the heterogeneous wireless networks. Accordingly, a seamless data service can be provided to a terminal in a service environment where a plurality of wireless communication systems is used.