Nanocomposites based on isotactic polypropylene (PP) and nanosilica (SiO(2)) were prepared using a co-rotating twin-screw extruder (TSE). The effect of operating variables, such as screw speed and screw configuration on the dispersion of nanosilica in the polymer matrix has been studied, using TEM imaging. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good nanosilica dispersion. Furthermore, the effects of filler loading and amount of a maleated polypropylene (PP-g-MA) compatibilizer on the degree of SiO(2) dispersion were investigated. The foaming performance of the composites was evaluated using a batch foaming simulation system, and an extrusion foaming setup that employed respectively N(2) and CO(2) blowing agents. Well-dispersed surface-modified hydrophobic SiO(2) particles acted as effective nucleating agents for foaming, when used at loadings below 1 phr.