Abstract: The microstructure and tensile properties of TIG welded joints of Al-Li alloy were investigated both in as-welded and different postweld heat treatment conditions.The results show that solid solotion strengthening played an important role in the as-welded condition,though the precipitation strengthening δ' phase formed already in the as-welded weld metal,but its effect was not apparent due to the lower volume fraction of δ' phase.So the strength ration of the welded joint/base metal (φ) was 64%.After artificially aging heat treatment,the precipitation strengthening effect increaced much due to the formation of more δ' phase and s' phase.Its φ value was increased up to 89%.The highest stength of the welded joints was obtained after solid solution and then artificially aged heat treatment.Due to the proper size of recipitation strengthening phases and their well distribution,the φ value was increased up to 98%.