In this study, effects of fiber surface treatments on mechanical behavior and fracture mechanism of glass fiber/epoxy composites were investigated experimentally. To change the composition of the glass and regenerate to the hydroxyl groups, activation pretreatment of heat cleaned woven glass fabric was performed using (v/v) HCl aqueous solution at different concentrations before silane treatment. The treatment of silanization of heat cleaned and acid activated glass fibers with gamma-glycidoxypropyltrimethoxysilane were performed. In this work, short beam shear test has been conducted to determine the performance of the acid treatment and the silane treatment in terms of the interlaminar shear strength. The silane coating on the heat cleaned glass fibers increased the interlaminar shear strength of the composite. However, the silane coating on the acid activated glass fibers did not improve the interlaminar shear strength of the composite. In addition, the strengths of the glass fabric specimens in tension and flexure were investigated. When the glass fibers are first treated with HCl solution and then with silane coupling agent, the tensile strengths of the composites decreased significantly. Scanning electron photomicrographs of fractured surfaces of composites were performed to explain the failure mechanisms in the composite laminates broken in tension.