The nonisothermal crystallization kinetics was investigated by differential scanning calorimetry for the nylon 6/graphene composites prepared by in situ polymerization. The Avrami theory modified by Jeziorny, Ozawa equation, and Mo equation was used to describe the nonisothermal crystallization kinetics. The analysis based on the Avrami theory modified by Jeziorny shows that, at lower cooling rates (at 5, 10, and 20 K/min), the nylon 6/graphene composites have lower crystallization rate than pure nylon 6. However, at higher cooling rates (at 40 K/min), the nylon 6/graphene composites have higher crystallization rate than pure nylon 6. The values of Avrami exponent m and the cooling crystallization function F(T) from Ozawa plots indicate that the mode of the nucleation and growth at initial stage of the nonisothermal crystallization may be as follows: two-dimensional (2D), then one-dimensional (1D) for all samples at 5-10 degrees C/min; three-dimensional (3D) or complicated than 3D, then 2D and 1D at 10-20 and 20-40 degrees C/min. The good linearity of the Mo plots indicated that the combined approach could successfully describe the crystallization processes of the nylon 6 and nylon 6/graphene composites. The activation energies (Delta E) of the nylon 6/graphene composites, determined by Kissinger method, were lower than those of pure nylon 6. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1381-1388, 2011