Polypropylene (PP)/clay nanocomposite was melt-compounded using high shearing/mixing and chaotic mixing, the former provided by kneading block sections in twin-screw extruder and the latter by a convective screw. Effect of mixing type on rheological behavior and microstructure of nanocomposites was investigated. Rheological property development along twin-screw extruder was also tested. By numerical simulation, shear strain was calculated. Based on rheological analysis, the relationship between the shear strain and microstructure of nanocomposite was analyzed. Results show that chaotic mixing facilitates the dispersion of clay in PP matrix. Along twin-screw extruder, the complex viscosity of samples is increased, and melt yield stress of end-obtained samples is decreased with increase of the feeding rate. Observed from transmission electron microscopy photomicrographs, a better dispersion of clay in PP matrix was found when feeding rate is lowest, and the total strain calculated is largest at the lowest feeding rate. It is deduced that higher strain in flow field is important to obtain better dispersion and properties of polymer/clay nanocomposites. POLYM. ENG. SCI., 51:2345-2352, 2011. (C) 2011 Society of Plastics Engineers