The influences of UV-induced photodegradation on the nonisothermal crystallization kinetics of polypropylene (PP) were investigated by differential scanning calorimetry. The Avrami analysis modified by Jeziorny, Ozawa method, and a method modified by Liu were employed to describe the nonisothermal crystallization process of unexposed and photodegraded PP samples. Kinetics studies reveal that the rates of nucleation and growth may be affected differently by photodegradation. A short-term UV-irradiation may accelerate the overall nonisothermal crystallization process of PP, but a long-term UV-irradiation should impede it.