A system using a packet network in a mobile communication system is provided, in which a home BTS provides a mobile communication service to an MS using a packet network as a backhaul network, a home BTS manager provides information necessary for providing the mobile communication services to the home BTS and manages the home BTS, a security gateway resides between the home BTS and upper network elements and protects a network of the mobile communication system against the packet network, a WSS performs a call control and mobility control function for the MS through the home BTS, and a WGW transcodes voice data transmitted from the MS via the home BTS.