Use of microcystins having a monocyclic heptapeptide structure in preparation of drugs for preventing or treating organ and tissue fibrosis diseases. Preferably, the microcystins are microcystin-LR with amino acids at positions 2 and 4 of a monocyclic heptapeptide structure thereof being leucine and arginine respectively, or are microcystin-RR with amino acids at positions 2 and 4 thereof being both arginine. Also provided is a method for inhibiting myofibroblast differentiation and collagen synthesis. The method is implemented by inhibiting a TGF-β/Smad signaling pathway by using one or more microcystins.
