The embrittlement of microalloyed and grain-refined high tensile strength steel plates, which are to be extensively used as structural components in nuclear reactors in India, was studied after irradiating to neutron fluences between 1.7 x 10¹⁷ and 1.0 x 10¹⁹ n.cm² (E > 1 MeV). The irradiations were carried out at less than 150°C. The results of room temperature tension tests and the instrumented impact tests over a range of temperature are presented. Irradiation stability of the steel is monitored by measuring the increase in yield strength and the elevation in the ductile-brittle-transition temperature after neutron irradiation. Attempts have been made to assess the extent of embrittlement as a function of neutron exposure. The results have been compared with both vintage and advanced pressure vessel steels.