Glass-fiber-reinforced epoxy and unsaturated polyester (UPE) composites were fabricated from diglycidyl ether of bisphenol-A (DGEBA) using 10% diethyl triamine (DETA) as a hardener and unsaturated polyester (UPE) using 1.5% each of methyl ethyl ketone peroxide (MEKP) and cobalt naphthanate as a catalyst and an accelerator, respectively. The fabricated composites were exposed to different aggressive environments, such as heat, water ageing, lubricating oil, fuel, and seawater. The exposed specimens were characterized by physical, chemical, mechanical, and thermal properties. A marginal increase (12%) in the mechanical properties in heat ageing, but a reduction in properties in other exposed systems of the epoxy and polyester glass-fiber-reinforced (GFRP) composites, were observed.