Three new micropeptins, micropeptin DR1056, DR1060 and DR1006 and three known metabolites, micropeptin SF909, aeruginosins 298A and B were isolated from the extracts of a Microcystis aeruginosa bloom material collected in Dalton reservoir, Israel. The planar structure of the compounds was determined by homonuclear and inverse-heteronuclear 2D NMR techniques as well as high-resolution mass spectrometry. The absolute configuration of the asymmetric centers of the amino acids was studied using Marfey's method for HPLC. The inhibitory activity of the compounds was determined for the serine proteases: trypsin, chymotrypsin, and elastase and for amino peptidase N.