High density polyethylene (HDPE) and calcium carbonate (CaCO3) nanocomposites with maleic anhydride grafted HDPE (manPE) as a compatibilizer were prepared via compounding in a twin-screw extruder. The CaCO3 are well dispersed in the HDPE matrix from the observation of transmission electron microscope. The isothermal crystallization kinetics was studied by differential scanning calorimetry and simulated by Avrami and Tobin models. The nucleation constants and fold surface free energy were estimated from Lauritzen-Hoffman relation. The results indicate that both manPE and well-dispersed CaCO3 particles would act as nuclei to induce heterogeneous nucleation and enhance crystallization rate. (c) 2007 Wiley Periodicals, Inc.