An apparatus for transmitting/receiving a signal in a communication system is provided. A Mobile Station (MS) spreads a transmission signal to generate a spreading signal, receives, from a Base Station (BS), information on a second spreading signal transmission region, extended from a first spreading signal transmission region, and maps the generated spreading signal to a subcarrier in the second spreading signal transmission region. A Base Station (BS) transmits information on a second spreading signal transmission region extended from a first spreading signal transmission region, for reception of a spreading signal, receives a spreading signal mapped to subcarriers over the second spreading signal transmission region, from an Mobile Station (MS), detects a spreading signal from the spread signal mapped to the subcarriers, and despreads the detected spreading signal to restore a transmission signal.