Huge amount of Portland cement is manufactured as a binder of concrete, and CO2 emitted in the production process causes one of major factors of global warming. Alkali-activated material (AAM) is generally synthesized by-products such as fly ash (FA) and blast furnace slag (BFS) with activators. AAM with high BFS content has short setting time, although it has great strength development. Ensuring appropriate setting time is an important issue in usage expansion of AAM which contribute to low environmental impact. The present study focuses on setting time of AAM produced using activator with caustic soda solution and water glass. The effect of mole ratio of SiO2/Na2O in water glass, BFS substitution rate and gypsum in BFS were investigated in this study. As a result, gypsum had no effect of delaying initial setting time, and AAM with higher mole ratio of water glass and lower BFS substitution ratio had longer setting time, although the extension effect of these mixture conditions on initial setting time was smaller than one on final setting time.