High density polyethylene/graphene nanocomposites were synthesized via in-situ polymerization technique using metallocene catalyst and methylaluminoxane (MAO) as co-catalyst. The non-isothermal crystallization of the nanocomposites was studied using differential scanning calorimetry (DSC). Modified Avrami, Ozawa and the model proposed by Mo et al. were applied in the analysis. The activation energy (Delta E) was calculated using the iso-conversional method proposed by Vyazovkin. The effect of degree of transformation and temperature on Delta E was analyzed. It was found that graphene nucleates the crystallization of HDPE by lowering Delta E as well as increasing the crystallization onset temperature (T-on). However, at later stages of crystallization, excess amount of graphene hinder the crystal growth rate thereby retarding overall rate of crystallization, observed from increase of t(1/2) and degree of super cooling. (C) 2014 Elsevier B.V. All rights reserved.