Duplex supporting apparatus and method in a base station system which supports a multi-antenna are provided. The duplex supporting apparatus in a base station system which supports K(.gtoreq.1)-ary sectors and M(.gtoreq.1)-ary antennas per sector, includes a plurality of channel cards for generating M-ary data to be sent to the M-ary antennas, exchanging part of the M-ary data with other channel cards, constituting a frame with part of the M-ary data and data received from the other channel cards, and providing the generated frame to a corresponding Radio Frequency (RF) module; and a plurality of RF modules for extracting the M-ary data from a frame of a corresponding channel card among the channel cards, RF-processing the extracted M-ary data, and feeding the processed data to original sectors/antennas.