As bridges and marine structures are being declared unsafe in increasing numbers, economical ways must be found to return such an infrastructure to its previous safe conditions. The use of repairing techniques with externally bonded FRP sheets and structural adhesives is increasing for concrete structure and aircraft because of high rigidity, lightweight and easy fabrication. This method will be able to be applied to repairing of ocean structures. If this method can be used, bonding strength is more important than an intrinsic strength of reinforcing materials. In this study, environmental durability of bonding strength between FRP sheet and steel were investigated in marine environment. Four kinds of CFRP sheets are prepared : four resins, epoxy, vinylester, isophtalic and orthophtalic polyester resin. An approach based on fracture mechanics was applied to evaluate bonding strength between steel members and FRP sheet. “Membrane Peeling” test was proposed and used to evaluate the influence of different surface treatment on bonding strength between concrete and FRP sheet. In this case, the bonding strength of steel member reinforced by epoxy resin was found to be twice as that of steel member reinforced by the others resin before these test specimens were immersed in seawater. On the other hand, steel member reinforced by epoxy resin got most decreased debonding strength after immersion in seawater for one month.