The objective of this paper is to clarify mechanical properties and delayed fracture mechanism of woven GFRP laminates which possess high corrosion resistance in hostile environment. GFRP used in this paper is consisted of acid resistant glass fiber and vinylester resin and the environment discussed are deionized water, hydrochloric acid (1.0 mol/l) and air at 80°C. Mechanical properties of GFRP decreased slightly with immersion into two solutions and decreased intensely after long-term immersion. The mechanical properties decreased regardless of the solutions and showed a tendency to saturate toward certain values. Strain and its growth rate of GFRP under constant tensile load increased with the increase of applied stress and with immersion into both solutions. Besides, delayed fracture occurred in both solutions and fracture time shortened drastically with the increase of applied stress and temperature and also decreased in the order in air, in deionized water and in hydrochloric acid. In addition, fracture surfaces of GFRP after delayed fracture were observed. It was concluded that the strength degradation of glass fiber aligned toward the loading direction lead to fiber break and result in delayed fracture of woven GFRP.