This paper describes a indirect complexometric method for the determination of mercury in the presence of co-ions, based on the selective masking ability of potassium iodide. To the mixture of mercury (II) and other metal ion solution, EDTA solution was added in excess of the metal ions present. The pH of the solution was adjusted to 5.0-6.0 using solid hexamine (10 +/- 2 g) and surplus EDTA was titrated with zinc sulfate solution using xylenol orange indicator. An excess of solid potassium iodide was then added to decompose the Hg-EDTA complex and the released EDTA was titrated with standard zinc sulfate solution. Accurate results were obtained for 4.5-80 mg (2.24 x 10(-5) M - 3.99 x 10(-4) M) of mercury with relative errors less than or equal to 0.4 %, standard deviations less than or equal to 0.07 mg. Sn(IV) and Au(III) interferes but can be masked using sodium fluoride. The method can be applied in the analysis of mercury in its alloys and complexes.