Composite modified asphalts with nanoscale calcium carbonate (CaCO3) and SBS were prepared by melt blending. Rolling thin film oven test (RTFOT) was carried out to study the aging property. The results demonstrate that both nano CaCO3 and SBS show homogeneous dispersion in the base asphalt, which lead to an improvement in terms of toughness, strength, and thermal stability. Influence of nano CaCO3 on the properties of SBS modified asphalts appears as a decreasing penetration, an increasing softening point, and a decreasing ductility. The anti-deformation ability under low temperature of nano CaCO3/SBS modified asphalts improved significantly. The softening point of nano CaCO3/SBS modified asphalt decreases after aging, in contrast to that of the base asphalt, which can be ascribed to the different rheological peoperties between nano CaCO3/SBS modified asphalt and the base asphalt. Compared with that of SBS modified asphalt, the anti-ageing property of nano CaCO3/SBS modified asphalts improved significantly. This indicates that nano structure of CaCO3 in modified asphalt can prevent oxygen from diffusing and permeating in matrix and the thermo-oxidative ageing of base asphalt and SBS slows down.