Nanocomposites of polypropylene and organically modified clays were compounded in a twinscrew extruder through two-step melt compounding of three components, i.e., polypropylene, maleicanhydride-grafted polypropylene (PP-g-MA), and organically modified clay. We examined the effects of PP-g-MA compatibilizers, including PH-200, Epolene-43, Polybond-3002, and Polybond-3200, with a wide range of maleic anhydride (MA) contents and molecular weights. The nanocomposites' morphologies and mechanical properties, such as stiffness, strength, and impact resistance, were investigated. X-Ray diffraction patterns showed that the dispersion morphology of the clay particles seemed to be determined in the first compounding step and further dispersion of the clays did not accur during the second compounding step. As the ratio of PP-g-MA to clay the increased, the clay particles became dispersed more uniformly in the matrix resin. As the dispersibility of the clays was enhanced, the reinforcement effect of the clays increased, but their impact resistance decreased.