A solid electrolyte of the present invention is represented by a general formula: Li.sub.xMO.sub.yN.sub.z, where M is at least one element selected from the group consisting of Si, B, Ge, Al, C, Ga and S, and x, y and z respectively satisfy x=0.6 to 5.0, y=1.050 to 3.985, and z=0.01 to 0.50. The solid electrolyte hardly deteriorates in a wet atmosphere.