A selective complexometric method is described for the determination of mercury(II) using sodium metabisulphite as a masking reagent. An excess of EDTA is added to mercury(II) solution containing associated diverse metal ions and the Surplus EDTA is back titrated at pH 5-6 (hexamine buffer) with standard zinc sulphate Solution Using xylenol orange as indicator. An aqueous solution of sodium metabisulphite is then added to displace EDTA selectively from H-EDTA complex and the released EDTA is then titrated against the same standard zinc sulphate solution. Reproducible and accurate results are obtained in the range 4-100 mg of mercury With a relative error < 0.26% and coefficient of variation less than or equal to0.40%. The method is useful for the analysis of mercury in complexes and alloy samples.