Alkali Activated Binders (AABs) are gaining prominence in the construction industry as sustainable alternatives to conventional cement due to their lower carbon footprint and enhanced durability. However, optimizing fresh and hardened properties of slag- fly ash-based AAB remains a key challenge. This study investigates the effect of borax as an admixture in slag-fly ash-based AABs, focusing on its influence on workability, setting time and mechanical strength. The slag- fly ash-based AAB for the study was prepared with 75% slag content activated using a combined activator of sodium silicate solution and 12M sodium hydroxide solution with an activator modulus (Ms) of 1 and 1.5. A series of experimental tests were conducted with varying borax dosages such as 2.5% and 5% by weight of binder to analyze its impact on the fresh properties and mechanical performance of the binder. The results indicate that borax significantly improves workability by increasing flowability of binder and extending setting time, which is beneficial for applications requiring longer handling periods. However, its influence on compressive strength and flexural strength of binder depends upon control factors such as slag to binder ratio and activator modulus of the alkali activator (SiO2/Na2O). The results shows that the addition of borax significantly influence early age strength attainment but only minimal or negligible reduction in strength at 28 days. Even at slag to binder ratio of 0.75 and activator modulus of 1.5, it was observed that the reduction in strength of AAB with borax is negligible. The study highlights the potential of borax as a chemical admixture for improving AAB performance, contributing to the development of durable and eco-friendly construction materials. Future research should explore long-term durability aspects and optimize borax dosages for specific engineering applications.