Bond and tensile durability of a glass fiber reinforced polymer (GFRP) bar used as flexural reinforcement in concrete beams has been investigated. Beams were pre-cracked and subjected to a constant sustained flexural load in indoor, outdoor, elevated temperature aqueous alkaline, freeze/thaw environments for up to 36 months. Crack widths were recorded during the sustained loading. Following conditioning, the beams were unloaded and subjected to eccentric 3-pt. flexure testing to determine bar/concrete bond behavior in the anchorage zone. From the other end of the beams, bars were extracted to evaluate their tensile behavior. Crack widths trended upward over time in all environments except freeze/thaw, where little change was seen. Average bond strength at the onset of bar-end slip and at ultimate was approximately constant or slightly increasing with sustained loading duration. The amount of bar-end slip at ultimate was nearly constant in the indoor environment, but decreased with duration in other three environments. Tensile strength decreased in the highly aggressive conditions involving much exposure to water, but not in the indoor or outdoor conditions. The modulus of elasticity did not change appreciably in any of the four conditions.