Many investigations have demonstrated that the addition of nanoscale particles could affect in-plane shear properties of the laminated composites. Besides, a variety of testing procedures were introduced to evaluate the in-plane shear properties of the multiscale composite materials. In the current research, Iosipescu shear, double V-notched rail, and off-axis tensile testing methods were used to measure in-plane shear modulus and strength of the glass/epoxy and carbon nanofiber (CNF) as 0.25 wt% CNF/glass/epoxy laminated composites. In-plane shear properties of the CNF/glass/epoxy specimens were increased in comparison with the neat glass/epoxy specimens using all three testing procedures. However, the improvements were not identical for all the testing methods. The maximum improvements in the in-plane shear modulus and strength recorded using off-axis tensile test method were as 11% and 15.6%, respectively. In the off-axis tensile test method, all in-plane stress components are activated in the fracture plane parallel to the fiber orientation which are responsible for the failure initiation and propagation. Consequently, enhancing the resin’s mechanical property and interface bonding quality using CNF could remarkably enhance the in-plane shear property of the CNF/glass/epoxy specimens. On the other hand, the special fiber orientation of the specimens in Iosipescu shear and V-notched rail methods prevents the reinforcing effects of the CNF particles to be effectively revealed.