The present invention provides a separator for fuel cell containing: a flat plate member; a gas passage-side member provided on one side of the flat plate member and having passages for passing a reactant gas therethrough; and a cooling water passage-side member provided on the other side of the flat plate member and having passages for passing cooling water therethrough, wherein the gas passage-side member and the cooling water passage-side member are formed from first and second conductive resin compositions which are different from each other, respectively, and the difference between the thermal expansion coefficient of the gas passage-side member in its thickness direction and the thermal expansion coefficient of the cooling water passage-side member in a direction perpendicular to its thickness direction is 25.times.10.sup.-6 /K or smaller, and wherein the flat plate member contains at least one of the first and second conductive resin compositions.