Chlorine dioxide was used to treat water treated with potassium ferricyanide to simulate ferricyanide wastewater. The ferricyanide was strongly oxidized by chlorine dioxide in the presence of sodium tripolyphosphate, with a final total cyanogen content of less than 0.011 mmol/L after the treatment. The treatment could be carried out successfully at ambient temperatures, and we established the following optimum conditions: a molar ratio of sodium tripolyphosphate to ferricyanide of 1.17, a treatment time of 60 min, and a molar ratio of chlorine dioxide to ferricyanide of 7.