Single-symbol maximum-likelihood (ML) decodable space-time block codes (SSDCs) can achieve a maximal symbol rate of 6/7 for multiple-input multiple-output (MIMO) communication system with five or six transmit antennas by using rate-efficient generalized coordinate interleaved orthogonal designs (RE-GCIODs).Unfortunately,there are many zero entries in the codeword matrix of RE-GCIODs.The zero entries result in high peak-to-average power ratio (PAPR) and also impose a severe constraint on hardware implementation.In this paper,for MIMO communication systems with five or six transmit antennas and one receive antenna,a new SSDC is proposed.By combining Alamouti code and orthogonal space-time block code (OSTBC),desirable properties like RE-GCIODs can be achieved and are derived,including maximal symbol rate up to 6/7,full diversity and single-symbol ML decodability.Moreover,by reducing the number of zero entries in the codeword matrix,the peak-to-average power ratio (PAPR) of our proposed code is lower than RE-GCIODs.Simulation results show that the proposed codes outperform RE-GCIODs under peak power constraint while performing almost same under average power constraint.