The invention provides a solid polymer fuel cell separator that is molded or formed of a resin composition comprising a thermoplastic resin, a conductive carbon black having a bulk density of at least 0.3 g/ml and a DBP oil absorption of up to 150 ml/100 g and optionally a conductive filler having a volume resistivity of less than 1 .OMEGA.cm. The invention also provides a solid polymer fuel cell separator production process involving injection molding of the resin composition.