In this work, a simple photometric method with high accuracy and precision for measuring trace amounts of free cyanide ion in aqueous solution is demonstrated. Under the evaluated conditions, we could determine CN− concentration in the range of 5–70 ppm easily. The work is based upon the photometric titration of CN− with Co(II) in the presence of 2,6-dichlorophenolindophenol (DCPIP) at λmax = 602 nm in aqueous solution. The optimal conditions, such as pH, ionic strength, and concentration of chromopher were evaluated. The interence effect of many other cations and anions studied and the results are given here. The optimized titration was successfully used to determine the concentration of free cyanide ion in aqueous solutions.