A rapid method for detection diarrhetic shellfish poisoning (DSP), a marine biotoxin, were developed. Monoclonal antibody against OA (okadaic acid) was prepared by using the technique of cell fusion. This antibody was applied in development the idc-ELISA (indirect competitive enzyme-linked immunosorbent assay) for detection of OA. Using OA-KLH as the immunogen to immunize BALB/c mice, splenocytes from the immunized mice were fused with murine myeloma cells. Three positive hybridoma cells strains that could secrete steadily anti-OA monoclonal antibody were obtained after three times of cloning. The idc-ELISA method with detection limit of 0.781 ng/ml was developed using 1# monoclonal antibody showing highest specificity against OA. Okadaic acid added was detected with average recoveries of 92.5% for scallop.