A direct-competitive time-resolved fluorescence immunoassay (TRFIA) for microcystin detection was established, which was based on europium labeled MCLR-BSA conjugant and microtiter plates coated with anti-mouse IgG. The optimal dilution of europium labeled MCLR-BSA conjugant is 1/50 and most appropriate titration of anti-microcystin-LR (MCLR) monoclonal antibodies is 100 ng/mL. The standard curve under the optimal conditions shows that the quantitative range is from approximately 0.05 ng/mL to 10 ng/mL. The detection limit of the method is 0.02 ng/mL for MCLR, recoveries for microcystin (> 94%) in quantitative range is satisfactory.