Three polypropylene (PP) matrices with different intrinsic toughness were used to study the morphology and mechanical properties of polypropylene filled with nano-sized calcium carbonate particles. PP1 was a homopolymer, PP2 was a propylene-ethylene copolymer, and PP3 was a mixture of PP1 and PP2 (PP1:PP2=1:1, weight ratio). The precipitated calcium carbonate (CC0.07) with an average particle size of 0.07 μm was used. Only the yield strength of PP1 nanocomposites filled with low CC0.07 contents (from 2 to 10 wt.%) could increase. When the CC0.07 content was appropriate, the impact strength of all three PP nanocomposites could improve. It was interesting that the intrinsic toughness of PP matrix would influence the toughening effect of the nanoparticles. Only in the case of the moderate matrix toughness (PP3 matrix), the nanocomposites could receive the highest extent of toughness increase (4.3 times that of matrix).