Objective. The purpose of this in vitro study was to determine the reinforcing effect of different forms and concentrations of E-glass fibers on impact strength of denture polymethyl methacrylate. Materials and method. A total of 91 rectangular specimens (84 specimens for test groups and seven for control group) of a heat-cured acrylic resin were fabricated. The test specimens were prepared by modifying the polymethyl methacrylate with the addition of different concentrations (2.5%, 3%, 4%, 5% by volume) of three types (chopped strand mat, woven and continuous unidirectional fibers) of E-glass fibers. The impact strength was evaluated using the Charpy method. Results. While the 5% continuous glass fiber added test group showed the highest mean impact strength, the lowest value belonged to the 2.5% woven glass fiber containing group. When the impact strength values of chopped strand mat and continuous unidirectional glass fiber added groups at all concentrations were compared with the control group, the differences were statistically significant. The impact strength values of the woven glass fiber added groups at all concentrations were higher than that of the control group. However, the difference was nonsignificant. Conclusion. The impact strength of PMMA was enhanced by including E-glass fibers, increasing parallel with the fiber concentration.