A lens module includes a lens set and a prism. The lens set has a first light emitting surface and a first engaging structure, wherein the first engaging structure is formed on the first light emitting surface. The prism is disposed adjacent to the lens set. The prism has a light incident surface and a second engaging structure, wherein the second engaging structure is formed on the light incident surface. The lens set and the prism are assembled with each other by engaging the first engaging structure with the second engaging structure.