In a guide for a transmission chain, a slide rail elongated in the direction of travel of the chain, and having a front surface for sliding engagement with the chain, is supported by a rail support which extends perpendicularly from the back side of the slide rail. The guide is formed by sandwich molding and comprises a glass fiber-reinforced polymer resin forming a core of the rail support, and a wear-resistant polymer resin forming both the slide rail, and a skin layer on the rail support, the skin layer of the rail support being unitary with the slide rail. A plurality of hollow, heat-dissipating, cavities extend inwardly from both sides of the slide rail in directions transverse to the direction of elongation of the slide rail.