Objective: The aim of this study was to illuminate the effect of different concentrations of titanium dioxide nanoparticles on the mechanical properties of heat polymerized acrylic resin. The tested parameters were flexural strength, impact strength, and microhardness. Material and Methods: 60 specimens were prepared according to the specific dimension for each test and allocated to two groups. Group (A) 45 specimens of conventional acrylic resin modified by addition of 1%, 3% and 5% TiO2 nanoparticles powder. Group (B) 15 specimens of unmodified conventional acrylic resin. Results: Flexural strength, impact strength, and microhardness were tested for both groups. The data was collected and statistically analyzed. Results: Flexural strength considerably decreased by increasing TiO2 concentration, meanwhile impact strength significantly decreased with increasing TiO2 concentration. The microhardness was significantly increased by increasing TiO2 concentration. Conclusion: Increasing TiO2 concentration was significantly improving microhardness and diversely affecting flexural strength and impact strength