The effect of alkali content (% K2O + %Na2O) on the mechanical properties of alkali activated blast furnace paste has been investigated. The paper presents the study on workability, compressive strength, split tensile strength and microstructure of alkali activated blast furnace slag paste specimens prepared by using of sodium silicate and potassium hydroxide solution as activators. The experimental results have indicated that the compressive strength, split tensile strength and workability of the specimens is significantly affected by the alkali content of the mix. The highest compressive strength achieved was 51.44 MPa. The mineralogical and micro structural changes were studied using XRD and scanning electron microscopy (SEM).