The quiescent isothermal crystallization kinetics of polypropylene was studied as a function of molecular weight (M-w), amount of ethene, and amount of maleic anhydride and acrylic acid grafting. Differential scanning calorimetry and polarized light optical microscopy were used to follow this kinetics. It was observed that the linear growth rate, G, decreased with the increase of M-w, but increased with the amount of ethene. In the grafted polymers, as the amount of grafting increased, G decreased. The fold surface free energy, sigma(e), was found to increase with the increase in M-w. The heterophasic and grafted polymers had sigma(e) values higher than the homopolymers. All samples showed spherulitic morphology, except the acrylic acid-grafted polypropylene that showed axialitic morphology.