When CNG, LPG, and other gas fuels were used for combustion in vehicles' engines, a large degree of valve seat wear was observed and it was difficult to provide the same wear resistance as for gasoline engines. Therefore, the mechanism of valve seat wear in gas fuel engines was analyzed and an alloy valve seat was developed. In addition to converting the matrix to an alloy, Co-Mo-Cr was used for the self-lubricating effect present in its hard particles. Also, in order to improve machinability, which is inversely related to wear resistance, a sintered alloy valve seat containing MnS was developed. As a result, wear resistance equal to that for gasoline engines was achieved.