Shear thickening fluids are being used for high-performance soft body armor, personal protection, and smart devices. In this work, the shear thickening behavior of polyethylene glycol (PEG) in the presence of silica AEROSIL 816 (slightly hydrophobic) and silica AEROSIL 200 (hydrophilic) nanoparticles (NPs) was investigated using rheological characterization in the steady-state flow mode. Significant differences in shear thickening behavior of the PEG/silica 816 NP and PEG/silica 200 NP were observed, signaling the importance of surface chemistry in the performance of the shear thickening nanofluids. Afterward, the hybrid suspensions of PEG/silica 200/silica 816 NPs at different ratios were prepared to investigate the effect of the combination of different nanoparticles on shear thickening behavior. To this aim, the viscosity curve of the hybrid samples was compared with silica 200/PEG and silica 816/PEG. The results showed that incorporation of two different nano-silica particles into the nanofluids increased both critical shear rate (i.e., onset of shear thickening behavior) and extent of shear thickening compared to that of the single nanofluids. Hence, mixing nanoparticles featuring different surface chemistries is an effective approach to enhance the shear thickening response of the nanofluids. In the last step of this work, the effect of pre-shearing on the rheological behavior of PEG/silica nanofluids was studied. To achieve this, samples were pre-sheared at three different shear rates (i.e., 10, 20, and 30 1/s). The result showed that pre-shearing changed the shear rate dependency of the viscosity for suspensions. In silica 200/PEG, the extent of shear rate and the critical shear rate decreased by increasing the pre-shear value.