The monoclonal antibodies against aflatoxin M1 were established. Spleen cells from Balb/c mice immunized with AFM1-oxime-BSA conjugate were fused with murine Sp2/0 myeloma cells. Three hybridoma cell lines secretine monoclonal antibodies against AFM1 were established after the fusion cells subcloned for 3-4 cycles. These antibodies were disignated as 3G2, 3G3 and 6G8, respectively. All of them belonged to the subtype of IgG1. The titres of the antibody in ascites ranged from 1:3.2 x 10(6)-1:20 x 10(6). There was no cross reaction between 6G8 monoclone antibody and other types of aflatoxin.