The pathogen causing severe acute respiratory syndrome (SARS) is identified to be SARS-Cov. It is urgent to know more about SARS-Cov for developing an efficient SARS vaccine to prevent this epidemic disease. In this report, the homology of SARS-Cov M protein to other members of coronavirus is illustrated, and all amino acid changes in both S and M proteins among all available SARS-Cov isolates in GenBank are described. Furthermore, one topological trans-membrane secondary structure model of M protein is proposed, which is corresponded well with the accepted topology model of M proteins of other members of coronavirus. Hydrophilic profile analysis indicated that one region (aa150～210) on the cytoplasmic domain is fairly hydrophilic, suggesting its property of antigenicity. Based on the fact that cytoplasmic domain of the M protein of some other coronavirus could induce protective activities against virus infection, this region might be one potential target for SARS vaccine development. The pathogen causing severe acute respiratory syndrome (SARS) is identified to be SARS-Cov. It is urgent to know more about SARS-Cov for developing an efficient SARS vaccine to prevent this epidemic disease. In this report, the homology of SARS-Cov M protein to other members of coronavirus is illustrated, and all amino acid changes in both S and M proteins among all available SARS-Cov isolates in GenBank are described. Furthermore, one topological trans-membrane secondary structure model of M protein is proposed, which is associated with the accepted topology of M proteins of other members of coronavirus. Hydrophilic profile analysis indicated that one region (aa150-210) on the cytoplasmic domain is fairly hydrophilic, suggesting its property of antigenicity. Based on the fact that cytoplasmic domain of the M protein of some other coronavirus could induce protective activities against virus infection, this region might one one potential target for SARS vaccine development .