Objective To study the mechanical properties of two kinds of composite resins reinforced by preimpregnated glass fibers.Methods Sinfony and belleGlass composite resinswere used tomake standard samples (25 mm×2 mm×2 mm) with and without glass fibers. After all specimenswere stored for24 hours in distilledwater at (37±1)℃, the flexural strength and flexural modulus were measured on a universal test machine.Results Both flexural strength and flexural modulus of Sinfony composite re- inforced by the glass fibers became significantly increased, whichwere (555.76±67.31) MPa and (12.59±3.06) GPa respec- tively, and 4.5 and 2.5 times muchmore than those of the specimenswithout glass fibers (P=0); the flexural modulus of belle- Glass composite became significantly increased, which was (14.10±2.88) GPa, and 0.9 time much more than the specimens without glass fibers (P=0), butthe improvement of flexural strengthwas not significantly.Conclusion Glass fibers can improve the mechanical properties of composite resins, but the reinforcement effect is different between different resins.