Abstract: Interferences for WO to ICP-MS direct determination of mercury in soil or sediment were studied.202WO+ was oxidized to higher oxide ion (218WO2+ or 234WO3+) for addition of oxygen in dynamic reaction cell.Interferences for WO were eliminated because 202Hg+ did not react with oxygen.When rejection parameter q was 0.75,and the oxygen flow was 1.9 mL·min-1,background of m/z 202 was reduced 100 times and low limit of determination (10σ) of 202Hg found was 0.5 ng·g-1.The proposed method was applied to the analysis of standard materials of soil or sediment,giving result that the method could eliminate mass interferences for WO to mercury.