An apparatus for retransmitting data at a retransmission request from a receiver by a transmitter in a CDMA mobile communication system including a turbo encoder with a given coding rate and initially transmitting systematic bits and parity bits obtained by encoding the data by the turbo encoder using one modulation mode among a plurality of modulation modes. A controller determines a modulation mode to be used between the transmitter and the receiver in response to the retransmission request. A distributor distributes coded bits obtained by encoding the data at the coding rate into systematic bits and parity bits. A selector selects coded bits transmittable by the determined modulation mode among the systematic bits and the parity bits at the initial transmission, if the determined modulation mode is different from the modulation mode used at initial transmission. A modulator modulates the transmittable coded bits into modulated symbols according to the determined modulation mode.