A valve timing control system for an internal combustion engine, comprises: an electric intake valve timing control apparatus to vary an intake valve timing with torque produced by an electric motor with electric power supplied through a power supply mechanism; and an electric exhaust valve timing control apparatus to vary an exhaust valve timing with torque produced by an electric motor with electric power supplied through a power supply mechanism. A heat generating portion in the power supply mechanism of the intake valve timing control apparatus is made of a heat resisting material whereas a heat generating portion in the power supply mechanism of the exhaust valve timing control apparatus is made of a material lower in heat resistance than the heat resisting material of the intake valve timing control apparatus.