Benzoic acid and sulphate ions in pesticide Lukangning are separated and determined on an ion chromatographic system with conductivity detector. The eluent contains 0. 75 mmol/L phathalic acid (pH4. 35) with a flow rate of 1. 5 mL/min. The separation column is a Shim-pack IC-A1 (4. 6mm id ×10cm) and the oven temperature is controlled at 40℃. The detection limits are 1. 3μg/mL and 0. 38μg/mL, the relative standard deviations 1. 82% and 1.24% and the recoveries 94. 6% and 95.2% for benzoic acid and sulphate ions, respectively.