In recent years, utilization of alkali-activated slag in place of Portland cement has been received a great attention of scholars, towards sustainable development. Sugarcane bagasse ash (SBA)–a by product of sugar industries, generated from combustion of bagasse in boilers for electricity production, has not been used effectively yet, causing environmental concerns. This paper presents a study on implementation of SBA to develop alkali-activated slag. Accordingly, SBA after passing through the No.100 sieve was uniformly mixed with ground blast furnace slag (GBFS) with different mass proportions (100/0, 90/10, 80/20, 70/30, 60/40) to prepared alkali-activated pastes. Sodium hydroxide and sodium silicate solutions were used to make alkali-based activators with variations of alkalinity (6%, 8%, 10%). Alkali-activated paste specimens were cured under room-air ambient. The testing results show that, setting times of the composites could be effectively adjusted by logically varying SBA dosage and sodium concentration. Mixture 90/10 exhibited the highest compressive strength and the lowest water absorption. Meanwhile, the mixture 80/20 had the lowest magnitude of shrinkage, which decreased by 1.3–3 times, compared to those of the mixture 100/0.