Abstract: The content of Hg in polypropylene sample was determined by isotope dilution ICP-MS. The sample was digested by high-pressure vessel with HNO₃/H₂O₂ as the solvent. By measuring ²⁰⁰Hg/²⁰²Hg abundance ratio and adding quantity of the spike, the content of Hg was determined. Moreover, the uncertainty of results were also analyzed and evaluated. The method indicates good accuracy, small uncertainty and less Hg loss during the pretreatment process. It is suitable for the certification of reference materials in national metrology institute.