This paper presents the preparation and characterization of geopolymer cement. Sodium hydroxide with different percentage (4%, 6% and 8%) with sodium silicate (5%, 10% and 15%) of the mass of blast furnace slag are mixed to prepare the activator. The slag is mixed with the activator of different concentrations to prepare the geopolymer pastes. The physicochemical and mechanical properties of the hardened pastes cured in water at room temperature for different time intervals up to 90 days are measured.XRD of some selected samples are made. The results indicate that alkali content has significant effect on the physicochemical and mechanical properties of the hardened pastes. Compressive strength, combined water contents and bulk density increase while total porosity decrease with increasing alkali concentration.