The irradiation effects of reactor vessel steels were studied by magneto-acoustic emission (MAE). Two commercial steels, A302B plate and A533B weld, and two model alloys were irradiated at four different conditions; high and low flux, two fluence levels (0.5 or 1 10(sup(19) n/cm sup (2)) and three temperatures (271, 288 and 307sup(o)C). For each material/condition and unirradiated control samples, MAE intensity in rms voltage with increasing magnetic field was measured. MAE waveform analysis can monitor the microscopic changes in the steel components subjected to neutron irradiation.