Geopolymer material is inorganic polymers that are generally synthesized from aluminosilicate materials, such as ferronickel slag. In this study, synthesis of geopolymer material using NaOH 7 molar and Na2SiO3 solutions with different Si/Al ratio to make paste. Paste is molded in a metal mold with dimensions of 5x5x5 cm3, then released from the mold and heated in an oven at 80 °C for 24 hours. The specimens that have been heated further left at room temperature for 28 days and then tested for compressive strengthand water absorption. The results indicate a trend compressive strength increases and water absorption decreases with increasing the Si/Al ratio. The optimum condition is obtained when Si/Al ratio is 3.5.