The effect of dynamic strain ageing (DSA) on stress corrosion cracking (SCC) of reactor pressure vessel(RPV) steels has been investigated. The experimental investigation was conducted on an A533B Class 1 steel subjected to slow strain rate test (SSRT) at a nominal strain rate of 2×10-6/s in stagnant primary water at 250°C. Various DSA responses of the steel were achieved by appropriate heat-treatment processes. The evaluation was made under identical environmental conditions. The results demonstrated that DSA enhanced the SCC which was consistently observed only in the steel that was heat-treated to give the most significant DSA hardening effect. The SSRT and fractographic evidence supports the previous observations based on the data analysis, i.e. there was a coincidence of temperature and strain rate between the DSA hardening and the susceptibility to environment-assisted cracking (EAC) of RPV steels. The mechanistic role of DSA and its interaction with other influential variables in the enhancement of SCC are discussed.