Thermal aging embrittlement of type 304L stainless steel weld is investigated on the basis of changes in microstructure, microhardness and electrochemical behavior after aging up to 20,000 h at 335, 365 and 400 °C. Spinodal decomposition and G-phase precipitation in the ferrite was observed after thermal aging. Aging led to increase in the hardness of ferrite phase while there was no change in the hardness of austenite. The changes in electrochemical behavior due to aging were studied using double loop electrochemical potentiokinetic reactivation (DL-EPR) test. Aging led to increase in the DL-EPR value which is attributed to Cr depletion in the ferrite phase.