This study investigated the strength development of cementless geopolymer concrete, which used ground granulated blast furnace slag(GGBS) as a source material, based on the mix proportions for alkali activated(AA) mortar from previous research. Cementless geopolymer concrete exhibited excellent early strength development, and the strength was about 1.5 to 3 times higher than ordinary portland cement(OPC) at age 1 and 3days. As strength property with mixing condition, the compressive strength was higher as water-to-binder(W/B) ratio was lower. Although the early strength was higher as the value of alkali quality coefficient QA was higher, the relationship did not continue in the long-term age. The equation proposed from investigation of AA mortar was applied to cementless geopolymer concrete with a slight modification and without additional variable analysis process, and the compressive strength predicted by this modified equation at 28days corresponded well with experimental results.