The use of seawater in cement-based concrete has debateable because it may increase the hydration rate but determinedly decrease the durability. Alternately, seawater can be used as alkaline activator solution in geopolymer however, very little is currently known about the use of seawater in geopolymer. This study investigated the effect of seawater as alkaline activator mix solution and curing media on the compressive strength of geopolymer paste. The mixtures varied based on the molarity of alkaline activator solution. Alkaline activators were prepared with two solutions: diluted water and seawater. A day after casting, steam curing method was conducted at 65°C for 2 hours and then immersed in seawater or normal water for 28 days. This study revealed that seawater in alkaline activator reduced the compressive strength by up to 25%. Applying temperature resulted the early age strength nearly comparable to the later age strength. Immersion the paste in seawater increased the strength up to 15%. The X-Ray Diffraction analysis shown the presence of chloride on the surface, consequently preserving the compressive strength without any reduction at 28 days of immersion. The Scanning Electron Microscopy analysis inside the geopolymer paste prepared with seawater shown the microstructure of quartz, mullite, hematite, and the presence of chloride spread around resulting the disruption of polymerization. The results indicated that seawater has the potential as an alkaline activator mix solution and curing media, compensated by requirement of higher molarity of NaOH.