In this study, polypropylene/silica (PP/SiO2) composites containing 5 wt% of untreated precipitated silica were compatibilized with different coupling agents like maleic anhydride-grafted polypropylene, glycerol monostearate (GMS), ethylene acrylic acid zinc ionomer and a second polymer phase of polyamide 6 (PA6). The composites were melt-compounded by two different processes: either by direct melt mixing or by dilution of a masterbatch (two-step mixing) in a twin screw extruder using both injected water and high shear stress as a new processing method. The various samples were characterized by Fourier transform infrared spectroscopy (FTIR), thermal analysis, morphological and rheological measurements in order to determine the compatibilizers effects between the matrix and the untreated filler. Hence, atomic force microscopy observations revealed that the untreated silica was dispersed more homogeneously in the presence of PA6 and GMS compatibilizers when water injection is used as one. However, the roughness values are lower in this case. FTIR analysis confirmed the existence of interfacial interactions between OH groups of SiO2 and polar groups of compatibilizers. The storage (G'), loss moduli (G '') and the dynamic viscosity of PP/SiO2 composites increased with the incorporation of PA6. Furthermore, the thermal stability of the compatibilized PP/SiO2 compounds enhanced significantly in the presence of water. An improvement in decomposition temperature of about 50 degrees C was obtained compared to uncoupled composites.