The magnetic properties of specimens of one heat of A533B nuclear pressure vessel grade steel have been examined in the as-received condition and after neutron irradiation to various fluence levels up to 4 × 10¹⁸ cm^-2 (E > 0.1 MeV) in the University of Illinois advanced TRIGA reactor core at two temperatures, approximately 120 and 260°C. The effect of certain heat treatments was also investigated. The magnetic properties were measured by an automated hysteresis curve-tracing method using a miniature transformer which incorporated the specimens in its core. Changes in magnetic hysteresis energy loss were correlated with neutron fluence in the case of certain irradiated specimens and with microhardness measurements in the case of heat-treated specimens. At the higher irradiation temperatures, no significant changes in either the magnetic hysteresis properties or the microhardness were noted for the present fluences. The relationship between the observed magnetic properties response and irradiation-induced embrittlement is discussed.