This paper evaluated the effects of chloride transients that may occur in boiling water reactor on stress corrosion cracking of pressure vessel low alloy steels. Crack growth rate and the delayed cracking response were enhanced by chloride transient in normal water chemistry while no chloride effect was observed in hydrogen water chemistry. The effects of chloride concentration, stress intensity factor, corrosion potential, and steel heat on the crack growth were discussed. The results from this work provide direct inputs to crack growth disposition models for low alloy steels, water chemistry guidelines and the plant operation practice during chloride transient.