Efflorescence in geopolymers can be a significant issue as the binder contains much higher soluble alkali metal concentrations than conventional cements. This paper reports the quantification method used to evaluate efflorescence potential on fly ash based geopolymer from the leaching behaviour of alkali metal in the solution followed by volumetric analysis. In this study, NaOH was used as the only alkaline activator. Geopolymer synthesis at higher molarity of NaOH gives higher percentage of excess sodium hydroxide content in geopolymer, indicating the higher potential of efflorescenece. Meanwhile, the effect of hydrothermal curing condition at the same alkaline molarity results in the lowest percentage of 4.84 excess sodium hydroxide content in geopolymers compared to others. The systems were subjected to 65 relative humidity at 80°C for 5 days. An optimum Na2O content along with hydrothermal curing condition can results in optimization of geopolymerization reaction. © 2016 The Authors.