A signal processing apparatus in a multi-input/multi-output (MIMO) communication system includes a transmitting end in which a code rate is differently set and a respectively different modulation method is performed at each antenna in consideration of a channel situation of each transmission antenna, coded bits are separately interleaved, and then collectively interleaved to transmit data, and a receiving end in which received data is collectively deinterleaved and then decoded and deinterleaved separately according to each reception antenna, and a channel situation of each signal received from multiple transmission antennas is estimated and fed back to the transmitting end. A different coding rates and modulation method are used at each transmission antenna and the spatial interleaving is performed to obtain a diversity gain in a space domain, and thus, the communication quality can be enhanced.