Abstract: The influence of glass fiber content and length on non-isothermal crystallization behavior of PP was investigated. The crystalline morphology was examined using polarized optical microscope. It showed that the glass fibers provided nucleating sites for crystallization. With increasing glass fiber content, the crystallization rate increased gradually and t1/2 decreased. As the length of glass fiber increased, the crystallization rate increased first and then decreased. The Avrami exponent was in the range of 2.99~3.40, which implied the nucleation mechanism and geometry of crystal growth of PP was not changed.