In this study, the mechanical and tribological properties of polymethyl methacrylate (PMMA)-based dentures strengthened by a low content of alumina (Al2O3) nanoparticles were evaluated. PMMA nanocomposites with different weight fractions (0.2, 0.4, 0.6, 0.8, and 1 wt%) of Al2O3 were fabricated, and a sample of pure PMMA was used as a control. Compression, hardness, and wear tests were conducted to investigate the effect of a low Al2O3 filler content on the mechanical and tribological properties of PMMA. The addition of Al2O3 filler improved the mechanical and tribological characteristics of PMMA. The highest elastic modulus and compressive yield strength (3.56 GPa and 138.21 MPa, respectively) were obtained using the PMMA sample with 0.6 wt% of nanoalumina, which represent an increase of 20.27% and 14.7%, respectively, compared with those of the pure PMMA. The fracture toughness and hardness were improved with the increase in the filler content until it reached 0.8 and 1.00 wt%, respectively. The tribological characteristics of PMMA also improved with the addition of Al2O3 nanoparticles. The least coefficient of friction (COF) and wear rate were obtained at a filler content of 0.6 wt%. Therefore, the addition of low amounts of Al2O3 to PMMA-based resins can improve their mechanical and tribological properties such as hardness, elastic modulus, fracture toughness, COF, and wear resistance.