An apparatus and method for transmitting data in a wireless communication system using Code Division Multiplexing (CDM) are provided. A code controller distinguishes a Walsh code used for spreading during data transmission and a Walsh code unused for spreading based on a signal-to-interference ratio required by the system, and separately provides the Walsh codes. A CDM multiplexer CDM-multiplexes input data using the Walsh code used for spreading, provided from the code controller. A code modulator modulates input data using the Walsh code unused for spreading, provided from the code controller. A multiplexer multiplexes outputs of the CDM multiplexer and the code modulator.