A projection lens unit for a pico-projector includes a plurality of plastic lenses and a single glass lens to minimize a change in focal length due to the heat generated inside the pico-projector. The lens array includes: a 1st lens with negative (−) refractive power, a 2nd lens with positive (+) refractive power, a 3rd lens with negative (−) refractive power, a 4th lens with negative (−) refractive power, and a 5th lens with positive (+) refractive power, wherein the 1st to 5th lenses are arranged in order from a screen upon which an image is projected, the 1st to 4th lenses are plastic lenses and the 5th lens is a glass lens.