Abstract: Microcystin is a class of cyclic hepatotoxin, which poses a great threat to human and animal health. Microcystin synthesis is regulated by a variety of environmental factors, and the synthesis efficiency of microcystin is directly determined by the amount of the corresponding synthetase and the catalytic rate, however, the relationship between protein expression levels of the microcystin synthesis gene cluster and environmental factors is still unclear. In this study, the mcyC and mcyI genes located in the two operons of the microcystin synthesis gene cluster were selected as representatives, using high-efficiency McyC and McyI polyclonal antibodies, detected the effect of iron stress on microcystin synthetase McyC and McyI protein expression levels by Western Blot. The result indicated that the protein levels of McyC and McyI within Microcystis aeruginosa PCC 7806 were consistent with the changes in the synthesis yield of toxins in vivo under iron stress, suggested that iron stress directly regulates the synthesis of the toxin by influencing the expression level of microcystin synthetase. This study provided the basis for further understanding the synthesis mechanism of microcystin.