Poly (methyl methacrylate) (PMMA) was used as a matrix for fabrication samples of polymer matrix composites (PMCs). The matrix was reinforcement by (Al2O3) powder with a volumetric ratio (20%) and an average grain size (40 ±5) μm. The manufactured samples were treated after conducting the surface treatment operations thermally with different temperatures (50,70 and 90 ⁰C) and with different treatment times (2,4,6,8, and 10 hours). The samples were subjected to a set of mechanical and microscopic tests, whereby the effect of thermal treatment on the bending fatigue life of the manufactured samples, and the effect of thermal treatment on the ability of the material to resist shear stress, flexural strength, wear, compressive resistance and impact resistance. The results showed that there was an improvement in fatigue life, shear stress, flexural strength, compressive strength, wear resist, and impact resistance after heat treated samples. The best fatigue life, shear resistance, wear resist, and flexural strength occurred for 6 hours post cure time, while it was observed that the best improvement in compressive resistance and impact resistance occurred after the passage of (4hours) of the post cure time. The results also showed that the best thermal treatment temperature is (T=70⁰C).