To　maximize　the　benefits　of　wire　arc　additive　manufacturing　(WAAM)　processes,　the　effect　of　post-deposition　heat　treatment　on　the　microstructure　and　mechanical　properties　of　WAAM　AZ80M　magnesium　(Mg)　alloy　was　investigated.　Three　different　heat　treatment　procedures　(T4,　T5　and　T6)　were　performed.　According　to　the　results,　after　T4　heat　treatment,　the　microsegregation　of　alloying　elements　was　improved　with　the　eutectic　structure　dissolved.　Samples　after　T5　heat　treatment　inherited　the　net-like　distribution　of　secondary　phases　similar　to　the　as-deposited　sample,　where　the　eutectic　structure　covering　the　interdendritic　regions　and　the　β-phase　precipitated　around　the　eutectic　structure.　After　T6　heat　treatment,　the　tiny　β-phases　re-precipitated　from　the　matrix　and　distributed　in　inner　and　outer　of　the　grains.　The　hardness　distribution　of　the　samples　went　through　T4　and　T6　heat　treatment　was　more　uniform　in　comparison　to　that　of　T5　heat　treated　samples.　The　tensile　test　showed　that　the　T6　heat　treatment　improved　the　strength　and　ductility,　and　the　anisotropy　between　horizontal　and　vertical　can　be　eliminated.　Moreover,　T4　treated　samples　exhibited　highest　ductility.　©　2021