A lens module includes a lens holder having a top wall that has a bottom surface, and a lens unit received by the lens holder. The lens unit includes a first lens adjacent to the top wall and a second lens attached to the first lens. The first lens includes a first object-side surface abutting against the bottom surface and a side surface abutting against an inner surface of the lens holder. The second lens includes a second object-side surface engaging with the first lens, and a jointing surface keeping a distance from the inner surface.