Tensile test, fracture toughness test, and stress corrosion cracking (SCC) test were conducted in order to evaluate the effect of thermal aging on the mechanical properties and SCC crack growth rate of shielded metal arc weld (SMAW) and gas tungsten arc weld (GTAW) of type 316L stainless steel. Thermal aging at 350 oC induced a moderate increase of ultimate tensile strength in both the welds, and the value of GTAW was higher than that of SMAW. The resistance to ductile crack extension of aged welds was lower than that of unaged welds. The fracture toughness of both aged and unaged GTAW tended to be higher than that of SMAW, although the ferrite content, main factor in the embrittlement, of GTAW was larger than that of SMAW. On the other hand, it was found that there was no significant difference in SCC crack growth rate between aged and unaged material in this study.