In a sulfuric acid medium, oxalate exhibits a strong catalytic effect on the oxidation of p-chloride aniline (ClBN) by dichromate, and the red oxidation product of ClBN has a maximum absorbancy at 520 nm. Based on this founding, a new FI method for determining oxalate was developed. A calibration curve of oxalate in the range of 0. 40-17.0 tg/mL was obtained. The detection limit was 0. 10 μg/mL. Sampling rate was 103-samples/h. The possible interference by the co-existing substances or ions was examined. This new method was applied to the determination of micro amounts of oxalate in real samples with satisfactory results.