Amino-functionalized nanosilica (ANS) was prepared from nanosilica (NS) modified by 3-aininopropyltriethoxysilane. The amine groups on the ANS surface could be positively charged at acidic environment. As a result, compared to NS, ANS presented better dispersion stability and stronger interaction with functional groups on acrylamide-based polymer. Three systems, such as nanoparticle free polymer (PAS), NS/polymer (PAS-S), and ANS/polymer (PAS-AS), were prepared, and the thermal degradations of these systems in distilled water after deoxygenation were carried out at 100 and 140 degrees C. The variations of apparent viscosity, degree of hydrolysis, and average hydrodynamic radius in the aging process were investigated, and the results indicated that ANS could both inhibit the hydrolysis of amide groups and protect the polymer backbone to avoid the rupture of polymer molecule. As a result, PAS-AS exhibited much better thermal stability at harsh environment. The relative viscosity for PAS-AS after 12 h degradation at 140 degrees C was 58.0%; however, it was only 14.9% for PAS. The long-term thermal degradations of three systems were also performed under a simulated oilfield condition. PAS-AS also presented the best thermal stability under low or high residual oxygen situations. Additionally, core flooding experiments show that PAS-AS solution has a higher oil recovery factor than PAS solution.