A lens assembly includes a first lens group, a second lens group, a third lens group, a fourth lens group, a fifth lens group, a sixth lens group, and a first reflective element. The first and third lens groups are with negative refractive power. The second and fourth lens groups are with positive refractive power. The fifth and sixth lens groups are with refractive power. The first, second, third, fourth, fifth, and sixth lens groups are arranged in order from a first side to a second side along an axis. The first reflective element includes a first reflective surface. A light from the first side sequentially passes through the first, second, third, fourth, fifth, and sixth lens groups to the second side. The first reflective element is disposed between the first lens group and the sixth lens group.