ABSTRACT : Cement industry is one of the major contributors to the emission of greenhouse gasses. So, efforts are needed to make concrete more environmental friendly by using fly ash which helps in reduce global warming as well as fly ash disposal problem. This paper presents study of effect of curing period on mechanical properties of fly ash based geopolymer concrete. The study analysis is the effect of Duration of treatment on compressive strength of Geopolymer Concrete. Geopolymer concrete is manufactured by replacing cement 100% with processed GGBS which is chemically activated by alkaline solutions like sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). In the present paper the effect of curing hours on Geo-polymer Concrete (GPC) specimens . Fly ash , silica fume and GGBS were used as binder, combined with an alkaline solution to form geopolymer paste instead of cement paste to bind the aggregates. The experiments were produced on GPC cubes for curing temperature of 60 ° C with curing period of 1day and 2 days . The constants used in the experiments were alkaline solution to binder ratio taken as 0.35, molarity of NaOH solution as 10M and ratio of sodium silicate to sodium hydroxide as 2.5. All the specimens were kept at one day rest period. The tests were conducted on each sample and results revealed that there is an increase in compressive strength for 90% slag + addition 10% Silica fume ) for both 12 and 24 hours of curing of GPC specimens. Results showed that increase in Duration of treatment to geopolymer ( Slag Only 100% )increased the compressive strength of GPC.