Phosphate　acid-activated　metakaolin　geopolymer　(PMG)　was　successfully　prepared　using　a　two-step　curing　method　and　the　thermal　stability,　pore　structure　and　moisture　adsorption　property　of　the　obtained　PMG　were　studied　by　techniques　of　thermogravimetry　(TG),　mercury　intrusion　porosimetry　(MIP)　and　dynamic　vapor　sorption　meter　(DVS).　TG　result　shows　that　thermal　decomposition　of　the　PMG　majorly　occurs　in　the　range　of　220-550　celcius,　much　higher　than　that　of　the　common　binder　of　C-S-H,　due　to　the　removal　of　the　chemically　bonded　water　and　the　water　content　of　the　PMG　is　around　16%.　MIP　measurement　indicates　that　the　porosity　of　the　PMG　is　13.6%　and　the　most　probable　pore　size　is　about　100　nm.　DVS　results　shows　that　the　water　adsorption　amount　of　PMG　powder　is　about　0.132　ml/g,　which　is　in　good　agreement　with　the　total　porosity　measured　by　MIP　test.