A lens assembly comprises a first lens and a second lens. The first lens includes a first central round portion and a first peripheral stepped portion surrounding the first central round portion. The first peripheral stepped portion comprises a downward-facing surface, a first supporting surface, and a first inclined surface interconnected. The second lens includes a second central round portion and a second peripheral stepped portion surrounding the second central round portion. The second peripheral stepped portion includes an upward-facing surface, a second inclined surface, a third surface, and a second supporting surface. The second lens is engaged on the first lens in a manner that the first supporting surface contacts the second supporting surface, the downward-facing surface is facing toward the upward-facing surface, the first inclined surface contacts the second inclined surface but a gap is defined between the first inclined surface and the third surface.