A regression model was constructed to elucidate the effects of various additives on the UV- stability of glass fiber reinforced epoxy (GRE) pipes by applying a four-factor central composite design (CCD) statistical approach. Four factors investigated were amount of UVabsorber, antioxidant, carbon black, and flame retardant. The ANOVA showed that most mechanical properties except for the hardness were a strong function of the amount of UV-absorber, carbon black, and flame retardant, while quite independent of the antioxidant content within the studied range (0-10%w/w). The amount of UV-absorber and other additives seemed to exhibit significant interaction effect on mechanical properties. The photodegradation of the GRE pipes was performed by an outdoor exposure and under simulated condition in Q-UV Lamp. The GRE pipes containing 2% UV-absorber, 1% antioxidant, 3% carbon black, and 10% flame retardant revealed better mechanical properties compared to the others.