The isothermal crystallization kinetics of nylon 6/graphene (NG) composites prepared by in situ polymerization was investigated by differential scanning calorimetry. The Avrami equation was used to study the crystallization kinetics. Comparing with nylon 6, it is found that the NG composites (NG-0.1, NG-0.5, and NG-1.0, where the number describes the wt% content of graphene) had higher crystallization rates; the crystallization rate increased remarkably with 0.1 wt% graphene. However, too many crystallization nuclei could not accelerate the crystallization process effectively. The t(max) values obtained from the plots of heat flow versus time were in agreement with the t(max) values calculated from the half time of crystallization when the graphene content was lower than 1.0 wt%, which means that the values of the Avrami parameters calculated from the half time of crystallization might be in better agreement with the actual crystallization mechanism than that determined from the Avrami plots. The n values of the NG composites ranged between 1.1 and 1.8, which can be interpreted as meaning both one-dimensional and two-dimensional crystallization growth occurred during isothermal crystallization process. The activation energies, which were determined by the Arrhenius' method, varied within the range from -188 to -142 kJ/mol. (C) 2013 Society of Plastics Engineers