This work aims to improve the rheological properties of partially hydrolyzed polyacrylamide (HPAM) for enhanced oil recovery by using silica (or silicon dioxide, Sio(2)) nanoparticles (NPs). Novel aqueous HPAM-based Sio(2) nanocomposites were formulated, and their rheological properties were investigated under different salinities, temperatures, and aging times. The results show that the inclusion of silica NPs significantly improved the viscosity and viscoelastic properties of HPAM especially under high temperature and high salinities. The NP/HPAM hybrid showed an impressive thermal stability at T = 80 degrees C after 12 days, and the viscosity reached similar to 5 times that of HPAM at 0.8 wt % NP loading. The Fourier transform infrared spectral data confirmed that the formation of a hydrogen bond between the carbonyl groups in HPAM and the silanol functionalities on the surface of silica NPs contributed to the improved performance. The oscillation test indicated that seeding Sio(2) remarkably facilitated the cross-links among polymer molecules and made the hybrids more elastically dominant. For a given HPAM concentration, it was observed that there was a critical nanoparticle concentration, which may indicate the absorption status of Sio(2) NPs onto HPAM, and the salinity also affected the viscosity value.