The susceptibility of 26H2MF and 34HNM structural steels (heat treated to obtain different microstructures) to hydrogen degradation is determined by slow-strain-rate tensile testing at 10−6 sec−1. The parameters such as ultimate strength, elongation to fracture, fracture energy, and reduction in area are evaluated. The substantial degradation of mechanical properties accompanied by brittle fracture is observed in 0.01 M H2SO4 + As2 O3 at a cathodic current density of 20mA/cm2. The degree of degradation of steel is correlated with the modification of microstructure as a result of heat treatment. The observed effects can be attributed to different tendencies of the obtained microstructures to hydrogen trapping.