In this study, mechanical properties of graphene nanoparticles (GNP) added glass fiber/epoxy nanocomposite specimens and the effect of GNP were investigated by applying the tensile test. Specimens were produced by vacuum assisted resin transfer molding (VARTM) method on the CNC device in standard sizes. The results obtained from the tensile test of the specimens prepared with the addition of GNP at the rates of 0.15%; 0.25%; 0.35%; 0.45% and 0.75% were compared with the sample without GNP. According to the test results, the tensile strength increases with the increase in the rate of GNP. The highest tensile strength was found when the GNP rate was 0.45%. At this rate, the tensile strength increases by 31.29% compared to the specimens without additives. However, increasing the rate of GNP more than 0.45% affects the mechanical properties negatively and causes a decrease in tensile strength. Finally, finite element analysis (FEA) was made by designing the produced specimens. FEA results were compared and found to be compatible with the experimental results.