Sodium bicyclic[2,2,1]heptane dicarboxylate (HPN-68) is a highly effective commercial isotactic polypropylene (iPP) nucleating agent. In this paper, isothermal crystallization behaviors of iPP nucleated with HPN-68 were investigated using differential scanning calorimetry (DSC). The calculation model of Lamberti based on the Avrami method was used for obtaining nucleus density from calorimetric crystallization curves recorded under isothermal conditions. A number of growth rate data have been obtained with the Lauritzen and Hoffman equation. General procedures to predict nucleus density by simple DSC measurements were described and applied successfully to iPP. Addition of HPN-68 shortened crystallization half-time (t (1/2)) and increased the crystallization rate of iPP, eventually the nucleus density of iPP nucleated with HPN-68 for finishing crystallization under higher crystallization temperature was larger than that of virgin iPP, leading to larger crystallization rate and shorter cycle time.