In multi-input-multi-output orthogonal frequency-division multiplexing systems, conventional channel-estimation techniques using comb-type training symbols give relatively large mean squared errors (MSEs) at the edge subcarriers. To reduce the MSEs at these subcarriers, a cyclic comb-type training structure is proposed. In the proposed cyclic training structure, all types of training symbols are transmitted cyclically at each antenna. At the receiver, the channel frequency responses that are estimated using each training symbol are averaged with weights obtained from the corresponding MSEs. Computer simulations showed that the proposed cyclic training structure gives more signal-to-noise ratio gain than the conventional training structure.