In　this　research,　metakaolin-based　geopolymers　were　synthesized　to　study　their　deterioration　in　marine　environment.　The　geopolymers　were　exposed　in　air,　seawater,　dry-wet　and　heat-cool　cycles　of　seawater　for　30,　60　and　90　days.　The　mechanical　property　of　the　geopolymers　was　characterized　through　compressive　strength　measurements,　and　their　microstructures　were　measured　by　X-ray　diffraction　(XRD),　scanning　electron　microscope　(SEM)　and　nuclear　magnetic　resonance　(NMR)　apparatus.　It　was　found　that　seawater　environment　inhibited　the　geopolymerization　reactions,　so　that　a　low　amount　of　tetrahedral　silicon　of　Q4(4Al),　Q4(3Al)　and　Q4(2Al)　were　formed.　©　2019　Brazilian　Metallurgical,　Materials　and　Mining　Association.