An apparatus and method interleaving symbols coded by a turbo encoder in a communication system that uses the turbo encoder for encoding transmission information into coded systematic symbols and at least one parity symbol pair, and maps the coded symbols using a second or higher modulation order before transmission. An interleaver controller performs a control operation of cyclic-shifting the systematic symbols among the symbols coded by the turbo encoder depending on a size of a physical packet to be transmitted, the number of transmission slots, and the modulation order, using an equation of (K.times.c+k)mod R, and cyclic-shifting redundancy symbols constituting the remaining size of the coded symbols to be transmitted, using an equation of floor{(K.times.c+k)/D}mod R. An interleaver cyclic-shifts input symbols under the control of the interleaver controller.