In this study, the environmental stress cracking (ESC) resistance of nano-SiO2 particle-filled polycarbonate (PC) was investigated at room temperature by using a fracture mechanical test method. Two PC-based nanocomposites with nano-SiO2 content of 1 and 4 vol% were compounded using a twin-screw extruder. The incorporation of nanoparticles into PC leads to an improvement in ESC resistance, which increases with increased filler loading up to 4 vol%. Fractography analyses suggest that the formation of cavities/debonding and localized microdeformation of matrix induced by nanoparticles as a result of energy dissipation are responsible for the improvement of ESC resistance.