Ag-Mo electrical contact material used in solenoid actuator showed high resistance during storage and with only a few switching cycles in service.Dark color erosion products were formed on contact surface causing high contact resistance.The failure contact was observed by SEM on surface and chemical contents of the dark area were checked by EDS.The results are compared with Ag-Mo material after oxidization at 500℃ and hydrogen sulfides corrosion at room temperature.Surface morphology observation and composition analysis suggested a mixture of Ag/S/O/C as well as Ag/Mo/O/C compounds were formed as high-resistance laver.