Abstract: The effect of nano TiO₂ modified epoxy coating on the properties of glass fiber/unsaturated polyester composite was investigated by UV-condensation accelerated aging test. The change of color and hardness of epoxy coating modified by different content of nano TiO₂ in UV-condensation environment was studied. Moreover, the color change, mass change, flexural and shear properties of glass fiber/unsaturated polyester composite without coating, with epoxy coating and 2wt% TiO₂ modified epoxy coating were investigated. The results indicate that the flexural strength of the glass fiber/unsaturated polyester composites without coating, with epoxy coating and 2wt% TiO₂ modified epoxy coating decreases by 14.7%, 10.0%, and 9.2% respectively after aging for 90 days in UV-condensation environment; the flexural modulus decreases by 5.9%, 5.4%, and 3.2%, respectively. Considering the interaction of UV, humidity and temperature, Gunyaev’s residual strength formula was modified, and the life of the glass fiber/unsaturated polyester composites was predicted.