Since characterization of in-plane shear properties of composite materials is necessary for designing composite structures, there are many methods for shear testing of composite materials. V-notched rail (VNR) shear test method is the latest method published as ASTM D7078 in 2005. Strain and stress states of VNR specimens were investigated numerically by adopting a commercial finite element software. The effect of measurement errors on the results was also analyzed. Although, the experimental programs were implemented based on standard considerations, the possibility of some errors was unavoidable. The sources of errors originated from misalignment of the specimen with respect to the loading axis, application of end loading instead of face loading and fiber misalignment. According to the obtained results, slipping of the specimen within the fixture grip plates had the most important effect on the results in comparison to two other error sources. In addition, fiber misalignment was another important source of erroneous results which needed to be considered during testing. Misalignment of the specimen with respect to loading axis showed the least effect on the shear properties of the specimens compared to others. Some other errors also affected the stress state of the specimen. However, our investigations showed that their effect on the shear properties was negligible. Finally, glass/epoxy specimens were evaluated experimentally by V-notched rail shear test method. Shear modulus of the V-notched specimens was almost equal with the modulus of three rail specimens. However, the shear strength measured by the V-notched rail shear test method was approximately 36% higher than that measured by the three rail test method.