Disclosed is an apparatus for determining transmit power of an uplink frame transmitted from a subscriber station to a base station and transmitting data in a mobile communication system in which a downlink frame, transmitted from the base station to the subscriber station, and the uplink frame are time division-duplexed (TDD). The apparatus includes a receive power measurement unit for measuring receive power of signals received from the base station; a transmit power controller for determining the transmit power of the uplink frame from the receive power measured by the receive power measurement unit and information related to receptions of an uplink frame, which is received from the base station; and a transmission radio frequency processor for performing radio processing so that the uplink frame is transmitted according to the transmit power determined by the transmit power controller.