A data translation apparatus is between a base station using an Internet protocol (IP) and a cell controller using an asynchronous transfer mode (ATM) data in a mobile communication system. The apparatus includes a plurality of line interface devices for performing a data connection with the cell controller, a physical layer processor for performing a physical layer process on a data received through the line interface device, a universal test and operations physical layer protocol interface for ATM (UTOPIA) switch for performing a switching process for translating and transmitting ATM data received from a cell controller and data received from an IP base station, a data translator for translating data to be transmitted to the UTOPIA switch into asynchronous transfer mode adaptation layer 0 (AAL0) data, and for translating data to be transmitted to the IP base station into Ethernet data, a plurality of repeaters for transceiving data between the IP base station and the data translator, a UTOPIA mapper for performing a UTOPIA interface on the data from the UTOPIA switch, a layer converter for converting the data from the UTOPIA interface to AAL0 layer or AAL2 layer data, and a controller for controlling operations of the layer converter, the UTOPIA mapper, and the UTOPIA switch.