In this study, St-MMA copolymer foams and (St-MMA)/silica nanocomposites foams were prepared using supercritical CO2 as a physical blowing agent. Microstructure and mechanical properties of the prepared foams were investigated in this study. In the first step, St-MMA microcellular foams were prepared in a predetermined composition and microstructural studies were conducted by SEM images analysis. Moreover, mechanical properties of the samples were examined in a compression mode. It was found that the incorporating silica nanoparticles led to produce foams with smaller sizes and uniform sell size distribution than St-MMA copolymer foams at the same condition. Consequently, the mechanical properties of the foam samples were improved when they were prepared using silica nanoparticles. Amount of absorbed gas for all samples was approximately equal 5wt% of St-MMA copolymer matrix.