Abstract: A simple and sensitive method for the measurement of residual oxalate in plutonium(Ⅳ) oxalate precipitation mother liquor was established by using ion chromatography. After the sample was diluted, at first, hydroxyurea（HU） was used to deoxidize MnO^-₄, then the sample flowed through H column to remove of cations, and was followed by the evaporation at 55℃ 5 L/min nitrogen purge to eliminate the interference of HNO₃. Finally, the disposed sample was determined by ion chromatography. The standard curves of oxalate show good linearity with r²=0.996 in the range of 0.01-50mg/L, and the detection limits of oxalate is 5.3μg/L. The proposed method was utilized to detect the trace oxalate in simulative plutonium(Ⅳ) oxalate precipitation mother liquor, and the result shows that the recovery of 0.5 mg/L oxalate is 88%-92%，s_r is 4.0%(n=6). This method is simple, accurate and highly sensitive. Therefore, it provides a viable method for determining the residual oxalate in plutonium(Ⅳ) oxalate precipitation mother liquor.