To improve the flexural strength and flexural modulus of polymethyl methacrylate (PMMA), copolymerization of PMMA with 10, 20, 30, and 40% (v/v) of either ethyl-methacrylate, butyl-methacrylate (BMA), or isobutyl-methacrylate (IBMA) was carried out. Test specimens were fabricated from heat-cured resin. The flexural strength was measured using a 3-point bending test. The chemical characterization and the copolymerization mechanisms of the copolymer resins were confirmed by H-1-NMR and FTIR. The flexural strength data were analyzed by applying two-way variance analysis. PMMA was reinforced by ethyl-methacrylate, BMA and IBMA copolymerization. Flexural strengths of the BMA and IBMA copolymers were significantly higher than those of the control group. Maximum flexural strength and modulus resulted from a 40% concentration of IBMA. The flexural strength and modulus values of all copolymer groups were found to be higher than those of the control group. The flexural moduli of the BMA and ethyl-methacrylate groups were similar to those of the control.