This paper presents an experimental investigation on the long-term mechanical performance, focusing on bending and compression of GFRP pultruded structural sections adopted as many structural constructions. Vinylester matrix has been used in combination with E-glass fibers. The degradation of the mechanical performance has been monitored through a process of accelerated artificial ageing by using aggressive environmental conditions, sea water set at different temperatures: 20, 40 and 60 °C, sea water wetting and drying cycles, alkaline solutions set at two different PH, 13.6 and 12.7 and acidic solution with PH = 3.5. In this study, flexural and compressive strength retention after about five months has been used as measurement of the imparted degradation and sea water absorption has been considered to define the diffusion coefficient and the activation energy for GFRP compositions. It was shown that the immersion of composites in alkaline solutions after 147 days, reduced the mechanical strength of sections more than the immersion in sea water and acidic solutions. And also results of the immersion in sea water solutions revealed that the strength reduction becomes larger in higher temperatures. The Arrhenius principle has been applied to estimate the long-term degradation of the GFRP profiles and predict the expected service life of such materials.