Nuclear pressure vessel steel, being ferromagnetic, provides a convenient means to monitor mechanical properties changes by measuring magnetic properties changes following exposure in a radioactive environment. Correlations between these two properties are examined in this work. Two types of nuclear pressure vessel steels are investigated: A533B and A533B weld in two irradiation circumstances. It is found that magnetic remanence and maximum permeability have dropped significantly after irradiation. The decrease of maximum permeability reflects increased difficulty of magnetization, which indicates more magnetic domain wall pinning sites were created. Since the mechanisms of pinning of domain wall movement and dislocation flow are similar, mechanical properties can be predicted. Presently, higher dose is still required to observe larger mechanical properties changes.