Resource shortage of fresh water and river sand due to the widespread increase of industrialization and urbanization can be reduced by using seawater and sea sand concrete (SWSSC), which has recently been proposed as an alternative to conventional ordinary Portland cement (OPC)-based concrete. Due to the high rate corrosion of traditional carbon steel when used as reinforcement for SWSSC and especially when subjected to seawater condition, fibre reinforced polymers (FRPs), as a corrosion resistant material may be used instead of carbon steel. Concrete-filled FRP tubes are known as one of the applications of using FRPs in construction. This study investigates the durability of SWSSC pultruded FRP tubes under seawater. Specimens are exposed to 1, 3, and 6 months of SWSSC solution as internal and seawater solution as external conditions at 25 °C, 40 °C and 60 °C temperatures. Tensile properties and degradation mechanisms of pultruded glass fibre reinforced polymer (GFRP) tubes were studied using tensile tests and scanning electron microscopy analyses.