Abstract: A direct competitive enzyme immunoassay for the quantitative analysis of chlorimuron-ethyl was developed. Polyclonal antibodies(PAbs) were prepared from rabbits immunized with hapten- protein conjugates. The titer of antiserum was 6.4×104,IC50 was 10.9 ng/mL. Chlorimuron-ethyl could be quantitated in the range of 0.4 ~295.4 ng/mL.Average recovery of chlorimuron-ethyl in river water was 87.9% ~115.7%.The cross-reactivity of PAbs of chlorimuron-ethyl with other analogues were 0.1% ~4.8%. This assay can be applied for the quantitation of chlorimuron-ethyl residue in river water.