The adhesive behavior of a diglycidyl ether of bisphenol-A epoxy resin modified by end-functionalyzed liquid polybutadiene was evaluated as a function of the temperature and of the time of immersion in distilled water. The neat epoxy and three modified systems were analyzed. Butt joints and single-lap joints were tested using an API X60 steel as substrate. The monophasic system obtained by reacting the epoxy monomer with hydroxyl-terminated polybutadiene (HTPB) functionalyzed with isocyanate groups (EPI) showed the best performance. The results show that this system is stable in respect to water degradation, but changes when exposed to temperature. Under the set of experimental parameters of time and temperature used, however, the adhesive strength increased with the temperature. For all epoxy formulations analyzed the fracture mode observed was of the adhesive type.