The influence of the spherulite size and distribution on the fracture toughness and Izod impact strength at different temperatures of controlled-rheology polypropylenes with 0, 154, 402, and 546 ppm of peroxide has been evaluated. As the peroxide content increased, the average spherulite size was enhanced and the distribution width reduced. The fracture toughness and the Izod impact strength were lowered with the peroxide content due to the diminution of the amorphous interconnections among the crystalline regions. Porosity seems to control the fracture behavior for the materials with the highest peroxide content. Besides, a considerable loss of ductility was observed ahead of the stable crack growth zone. Below the glass transition temperature, the impact strength underwent a sudden drop with the temperature, more remarkable as the molecular was higher. The main mechanism of deformation and failure consisted on the formation of crazes, stretch out, and a final collapse through the interspherulitic zones. POLYM. ENG. SCI., 52:805-813, 2011. (C) 2011 Society of Plastics Engineers