A projection lens comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens, wherein the first lens, the second lens, the third lens, the fourth lens and the fifth lens are arranged in order from the enlargement side to the diminution side. Diopter of the first lens, the second lens, the third lens, the fourth lens and the fifth lens is respectively negative, negative, positive, negative and positive. The diopter of the fourth lens is larger than that of the first lens and the second lens. Refractive index of the fourth lens is Nd and focal length of the fourth lens is f4. The focal length of fifth lens is f5. Due to the fact that the projection lens meets 0.45<|f4/ (f5*Nd)|<1.2, the projection lens has the advantages of being good in imaging quality and small in size.