Glass fiber reinforced materials are particularly attractive for transportation industries because of their high strength/mass ratio and their low cost compared to other materials. Therefore, the composite material system used in this study consists of polyester resin layers reinforced with E-glass fabrics. In this paper, the effect of mixed-mode loading on fracture parameters of glass reinforced polyester composite specimens is investigated both experimentally and numerically. Geometric factors were calculated for modified Arcan specimen using finite element analysis. The finite element results indicated that for loading angles close to pure mode-II loading, a high ratio of mode-II to mode-I fracture is dominant and there is an opposite trend for loading angles close to pure mode-I loading. According to experimentally measured fracture toughness for glass/polyester, the opening-mode and shearing mode interlaminar critical strain energy release rates, were found. Results indicated that the interlaminar cracked specimen is tougher in shear loading condition and weaker in tensile loading conditions.