The polypropylene (PP)/ poly(phenylene sulfide) (PPS) in-situ microfibrillar composites were prepared by the melt blending technology using a single screw extruder. Maleic anhydride grafted polypropylene (PP-g-MAH) is used as the compatibilizer. The rheology was characterized on capillary rheometer, and thermal behaviors of the PP/PPS were investigated by DSC. The experiment results reveal that the melting PP/PPS composites conform to the law of Non-Newton and show typical shear-thinning behavior. The viscosity of PP/PPS composites is nearly independent of the PPS concentration at 270°С and 280°С , respectively. However, the contents of PPS have an influence on shear viscosity of the PP/PPS at 290С and 300°С . The DSC results exhibit that the crystallization temperatures (TC) of PP in the composites are higher than that of the pure PP, and the TC of PP increases slightly with increasing PP content in the composites. Moreover, the melting temperature of PPS in the composites decreases slightly with increasing PP content.