Abstract: The effects of ultraviolet A (UVA) irradiation on properties of carbon fiber (CF) reinforced epoxy resin composites were discussed. UVA irradiance from the sunlight indoor and fluorescent lamp was investigated. After UVA exposure at the irradiance of 200 μW·cm^-2, the changes of mechanical properties and surface properties of CF reinforced epoxy resin composites by XPS, contact angle, nano-indentation, and atomic force microscope (AFM) were studied. The results show that UVA irradiance from the sunlight reaches the maximum value at 14: 00 on the clear days in spring and summer and the maximum value is 375 μW·cm^-2 at the window and sharply decreases to 30 μW·cm^-2 at 1 m far from the window. To the fluorescent lamp of 40 W, UVA irradiance is 87.3 μW·cm^-2 at the lamp and 5.4 μW·cm^-2 at 1 m far from the lamp. After UVA exposure of 45 days, there are no obvious changes on the interlaminar shear strength (ILSS), bending strength and tensile strength. CF reinforced epoxy resin composites have an oxidation on exposed surface and show increasing surface hardness and roughness.