In this paper, the isothermal crystallization kinetics of pure isotactic polypropylene (iPP) and iPP with 5% AB(3) hyperbranched polymer (HBP) added had been investigated by differential scanning calorimetry (DSC). During isothermal crystallization, the crystallization rate of the blends was higher than those of iPP remarkably. Moreover, the value of t(1/2) became smaller with increasing the HBP molecular weight in blends, however, the crystallization rate of the blend decreased when the higher molecular weight HBP ((M-n) over bar = 12,500) was added. The crystallization rate of the blends was more sensitive to temperature than that of iPP. An increase in the Avrami exponent may be attributed to the fractal structure of hyperbranched polymer.