Micropeptins 478-A and -B, plasmin inhibitors, were isolated from the cultured cyanobacterium Microcystis aeruginosa (NIES-478). Their structures were elucidated to be 1 and 2 on the basis of 2D NMR data and chemical degradation. These cyclic depsipeptides inhibited plasmin potently with IC50 Of 0.1 and 0.4 mu g/mL, respectively.