One of the advanced oxidation processes, the Oxone process, was studied to determine its effects on the decolorization of Reactive Black 5 (RB5) in an aqueous solution. Ferrous ion was chosen as the transition metal due to its potential catalytic effect and wide availability in dye containing industrial effluents. The effects of the operating parameters such as Fe(II) and Oxone concentration, initial pH, and temperature on the process performance were investigated. The optimum conditions were determined as: 0.5 mM of Oxone concentration, 0.5 mM of Fe+2 concentration, a pH of 5, and a temperature of 30 degrees C. At these conditions, the decolorization efficiency was 78%. Based on the results, it can be concluded that application of the Fe+2/Oxone system is very beneficial for a good decolorization efficiency in a very short time.