Abstract: Calcium carbonate (CaCO3) particles with cubic, spindle and spherelike morphologies were used as supporters to load heptane diacid as a βnucleating agent.The thermal behaviors and mechanical properties of PP blends with pure CaCO3 and heptane diacidloaded CaCO3 were investigated by differential scanning calorimetry and universal testing machine.The resultsindicated that the addition of CaCO3 improved the stiffness of PP blends, and the spindle CaCO3particles presented the least effect on mechanical properties.The incorporation of heptanediacidloaded CaCO3 not only improved the impact toughness of the blends but also generated a significant β-form nucleation effect on PP domain.The cubic CaCO3 particles could maintain a good stiffness for the blends, whereas the spindle CaCO3 particles exhibited the best toughening effect.The PP/sphere-like CaCO3 blends achieved a maximum improvement in impact strength up to 5.57 kJ/m2 compared to pure PP with the impact strength of 4.48 kJ/m2.On the other hand, the toughness of the blends was improved significantly with a decrease of the particle size of heptanediacid-loaded CaCO3.