In recent years, wind turbines have been increasingly adopted as a clean power generation system on a global scale, especially in European countries. Many studies have been conducted focusing on glass fiber reinforced plastics (GFRP) used for wind turbine blades. The fracture morphology of GFRP is dependent on various factors, such as load conditions, shapes of specimens, and manufacturing methods, in addition to the material properties and microscopic structures of fibers, resins, and interfaces; thus, the understanding of the mechanical behavior of GFRP is extremely important. Furthermore, fatigue strength and environmental effects must also be considered for the practical application of GFRP. However, there have been almost no studies focusing on both the mechanical behavior and fatigue strength of GFRP. In our study, an accelerated exposure test was conducted for GFRP and its matrix epoxy resin by using an ultraviolet (UV) irradiation device. Then, a tensile test and a fatigue test were carried out for the irradiated specimens to examine mechanical behavior changes in relation to the UV irradiation time and observe the fracture surfaces using an electron microscope. The test results show that the epoxy resin tends to lose its strength with UV irradiation while GFRP tends to slightly gain its fatigue strength with UV irradiation. This observation can be explained by concluding that the UV irradiation to GFRP reduces the interfacial strength between the fiber and the resin, resulting in peeling, which prevents cracks in the resin from growing across the interface.