Abstract: PP/PLA/CaCO3 compounds were prepared by a melt blending method, and the effects of PLA and CaCO3 nanoparticles on the mechanical properties, thermal property, rheological behavior and crystallization of compounds were investigated. The results indicated that the mechanical properties of compounds were improved with the addition of PLA due to the formation of a PLA continuous spatial network in the PP matrix. The compounds achieved optimum comprehensive mechanical performance when 20 wt% of PLA was introduced. Their tensile strength and impact strength increased by 5.1 % and 54.4 %, respectively, but the elongation at break decreases by 62.5 % compared to pure PP. A significant improvement in mechanical properties is ascribed to the “ball bearing” and nucleation effects of CaCO3 in the PP matrix. The CaCO3 nanoparticles were observed to be distributed in the PP/PLA matrix uniformly at a content of 15 wt%, leading to an optimum grain refining effect accordingly. The PP/PLA/CaCO3 ternary compounds obtained an increase in tensile strength by 15.2 %, in elongation at break by 2.7 % and in impact strength by 5.6 % compared to PP/PLA binary compounds.