Aim: To evaluate flexural strength (FS) and micro-hardness of poly(methylmethacrylate) (PMMA) denture base material modified with Zirconium oxide (ZrO2), titanium oxide (TiO2) and zinc oxide (ZnO) nanoparticles powder with different concentration (1.5, 3 and 5% ) Subjects and Methods: Test specimens of PMMA of dimensions (65 ×10 × 2.5 mm) were made from heat-cured acrylic resin served as control group Another nine group were made of PMMA containing 1.5, 3, and 5% (w/w) (ZrO2), (TiO2) and (ZnO) nanoparticles. Two types of mechanical tests were performed on the samples: flexural strength and hardness. Results: Statistical analysis results revealed that non-significant increase in flexural strength of heat cured reinforced with ZrO2 Nps and ZnO Nps for all concentrations. While adding 1.5% and 5% of TiO2 Nps showed significant increase in flexural strength but 3% showed significant decrease values. Results revealed that non-significant decrease in hardness of heat cured reinforced with ZrO2 Nps ,TiO2 Nps, and ZnO Nps for all concentrations except 3% of heat cured reinforced with TiO2 Nps which showed non-significant increase in hardness. Conclusions: It was discovered that adding of 1.5and 5% Tio2 Nps to the used denture base materials would improve the flexural strength of the denture base materials. Also, adding 1.5, 3 and 5 % ZrO2, Tio2, and ZnO Nps reduces the microhardness.