The polymeric materials, which have been generally considered to be good corrosion resistant material, are also degraded according to environments. The degradation behavior of polymeric materials can be classified into physical and chemical process. The later behavior in which molecular chain are cut chemically are called as corrosion. In this paper, the behavior, form and mechanism of corrosion of thermosetting resins used as matrix of GFRP (glass fiber reinforced plastics) under several solutions are mainly reviewed based on our experiments. The degradation behavior of GFRP are also mentioned briefly.