A two-dimensional subchannel assigning method and apparatus in a time-frequency domain where a plurality of subcarriers are arranged along a time domain with a plurality of symbols and along a frequency domain with a plurality of subbands in an OFDM communication system. In the subchannel assigning method, the plurality of subcarriers are divided into a plurality of frequency bands and the frequency bands are grouped into the subbands. A plurality of groups are generated by dividing each of the subbands in the frequency domain by the number of the symbols in the time domain. Subcarriers selected from the respective groups in each of the subbands are assigned as an AMC subchannel to which an AMC scheme is applied.