The nonisothermal crystallization kinetics of poly(propylene) (PP), PP-organic-montmorillonite (Org-MMT) composite, and PP-PP-grafted maleic anhydride (PPg-MAH)-Org-MMT nanocomposites were investigated by differential scanning calorimetry (DSC) at various cooling rates. Avrami analysis modified by Jeziorny and a method developed by Mo well-described the nonisothermal crystallization process of these samples. The difference in the exponent n between PP and composite (either PP-Org-MMT or PP-PP-g-MAH-Org-MMT) indicated that nonisothermal kinetic crystallization corresponded to tridimensional growth with heterogeneous nucleation. The values of halftime, Zc; and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PP and composites, but the crystallization rate of composites was faster than that of PP at a given cooling rate. The method developed by Ozawa can also be applied to describe the nonisothermal crystallization process of PP, but did not describe that of composites. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. The results showed that the activation energy of PP-Org-MMT was much greater than that of PP, but the activation energy of PP-PP-g-MAH-Org-MMT was close to that of pure PP. Overall, the results indicate that the addition of Org-MMT and PP-g-MAH may accelerate the overall nonisothermal crystallization process of PP.