Ferronickel slag is a secondary product from nickel ore smelting that containing many valuable metals such as nickel, cobalt, iron, even rare earth elements. This research is conducted to become the solution to the environmental issues that happened because of this slag and the valuable metals that wasted because there is no further processing of the slag. In this experiment, ferronickel slag is first given an alkaline fusion using sodium carbonate to remove silica that has a big amount in the slag and followed by the hot water leaching to separate the silica. Then, the hydrometallurgy process is started using the sulfuric acid with various concentrations such as 0.2M, 0.4M, 0.6M and 0.8M with the various time that is 15, 30, 60, 90 and 120 minutes to get the most effective condition to dissolve the nickel. The sample and result of this experiment are characterized by Inductively Coupled Plasma process to know how much the nickel and cobalt dissolve and can be collected to become a new product. Sample characterization showed the presence of Ni 0.1013% and Co 0.0041% The result of this research is 0.2M H2SO4 and 15 minutes of leaching is the best condition to make the highest % of nickel extraction.