The commercial glass fiber mat (from Hankook Fiber Co., Ltd.) was impregnated by polypropylene (5030 from Daehan Petrochemical Co., Ltd.) and the change of their impact strength and fracture surface were examined as a function of the processing conditions. The maximum processing temperatures of 180℃, 200℃, and 220℃ were tested. The specimens were preheated for 1,2 and 3 minutes, and then they were pressed for 0.5, 1 and 2 minutes with the applied pressures of 0.2 and 0.4 MPa. The highest impact strength was obtained with the specimens which were impregnated at 220℃ with 1 minute of pressing and 0.2 MPa of applied pressure after 2 minutes of preheating. The effect of recrystallization was obscure in this case. The severe thermal gradient in the specimen during cooling was detrimental to the impact strength