Abstract: Nanocomposites consisting of polypropylene homopolymer filled with in-situ graf ted nano-silica wereprepared by a conventional melt compounding technique. The influence of processing conditions on the mechanicalproperties of the nanocomposites was discussed. The mechanical performance , crystallization behaviors , morphologyand dynamic mechanical behaviors of the nanocomposites were studied. It can be concluded f rom the result s that thenotched Charpy impact st rength is significantly increased and a toughening effect can be attained by adding low loading (volume f raction ≤1.36 %) of the in-situ graf ted nanoparticles. Meanwhile , the tensile st rength can also beincreased. The reasonable processing conditions of the mixer can be set as 180 ℃for 10 min with the rotation speedof 60 r/ min. Studies of the crystalline characteristics indicate that addition of nanoparticles increases the rate of crystallization of PP. Filler/ mat rix interaction is enhanced due to interdiffusion and entanglement between the graftingpolymer and the mat rix , which is also emphasized by studies of the dynamic viscoelastic behavior and elucidates thetoughening and reinforcing mechanism of nanoparticles.