Abstract: In this study, a rapid and high sensitive direct competitive enzyme- linked immunoassay ( dc- ELISA) method based on the antigen labeled by Horseradish Peroxidase ( HRP) was established, which could be applied to the detection of 3- amino-2- oxazolidinone ( AOZ) that is a metabolite of furazolidone in real sample.In the direct competitive assay, monoclonal antibody was bound on the surface of a microtiter plate, then the standards ( or the sample) competed with CPAOZ antigen for the antibody binding sites.Calibration curve was prepared for 3- ( 4-carboxyphenyl) methyleneamino- 2- oxazolidinone ( CPAOZ) , the IC50 of dc ELISA was 0.08 μg / L, the limit of detection was 0.015 μg / L, detection range was 0.025 ⁰.5 μg / L. The recoveries of all kinds of samples were range from 82.0% to 121.0%.There was almost no cross reaction with other drugs of similar construction.The conclusion suggested that the AOZ- ELISA was a great method with high sensitivity for detecting AOZin samples.