Abstract: Neptunium is the raw material for ²³⁸Pu preparation. The accurate determination method of neptunium with accurate and clear traceability is very important for the extraction process of neptunium and the preparation of neptunium standard material. A novel method for accurate and precise determination of neptunium was developed. First neptunium was oxidized to Np(Ⅵ) in 1.0 mol/L sulfuric acid solution by silver(Ⅱ) oxide and excess silver(Ⅱ) oxide was destroyed by sulfaminic acid, then Np(Ⅵ) was titrated to Np(Ⅳ) by Fe(Ⅱ), finally excess Fe(Ⅱ) was re-titrated by standard potassium dichromate solution. When neptunium is about 5.0 mg, a good precision is achieved with the relative standard division (RSD) of 0.04%. The method is clearly traceable, simple, precise, accurate and can be explored to prepare neptunium standard materials.