Abstract: Objective To establish an indirect competitive enzyme-linked immunosorbent assay for the detection of medroxyprogesterone acetatere sidue.Methods Medroxyprog esterone acetate(MPA) was activated by carboxym ethyl hy droxy lamine hemi-HCL to form MPA-3-10-carboxymethyl oximel.The hapten was coupled to bovine seruma lbumin(BSA) with diisopro pylcarbodimi ide method to synthesize artificial mimunogen.The monoclonal antibody(McAb) against MPA was prepared and identified with routine methods.Indirect competitive enzyme-linked mimunosorbent assay(ciELISA) based on McAb was developed for the detection and estimation of medroxyproge sterone acetate residue in aquatic products. Results The artificial antigen MPS-BSA was confirmed by MALDI-TOF and its molecular weight was 76 045.656 3.The couple ratio of MPS-BSA was 25.71.The optmial concertration of the coating an tigen(MPS-OVA)and that of McAb against MPA was 1ug/ml and 1:40 000,respectively.Linear detection of ciELISA covered a range from 0.2ng/mL to 200ng/mL(R² =0.9707) with a sensitivity of 0.133ng/mL.The intra-assay and inter-assay coefficients of variation were 3.125% and 3.557 %,respectively.And the average fortified recovery of the method was 80.5%-101.00%.ELISA had 0.26%,10.67% of cross-reactivity with megestrol and medroxyprog esterone acetate,respectively.There was nocross-reac tivity with other antibiotics.Conclusion The indirect competitive enzyme-linked immunosorbent a ssay was established, which could be used to detect residues of medroxy prog esterone acetate in aquatic products.