Introduction: Poly (methyl methacrylate) has several disadvantages (poor mechanical properties) like impact and transverse strength. In order to overcome these disadvantages, several methods were used to strengthen the acrylic resin by using different fibers or fillers. This study was conducted to evaluate the effect of treatment fiber on the mechanical properties of poly (methyl methacrylate) denture base material. Materials and methods: Specimens were prepared from polymethyl metha acrylic (PMMA), which was divided into 4 groups based on the presence of fiber (first group without fiber as control group, second group with salinized polyester fibers, third group with salinized polyamide fibers and fourth group combination of salinized polyester and salinized polyamide fibers). Results: The results show that the highest mean values for all tests included in the study appeared in Group IV (combination of salinized polyester and salinized polyamide fibers) except for the surface roughness test the highest mean values were found in Group III (salinized treated polyamide fibers), and only polyamide fiber slight improved roughness and other groups have no effect on surface roughness. Conclusion: The addition of salinized treated fiber (polyester, polyamide, and combination of both fiber) improve transverse, impact strength and hardness properties of denture base material and has no effect on the surface roughness.