Three protease inhibitors (BWI-1, BWI-2 and BWI-4) from buckwheat seeds were purified to homogeneity and characterized. Their molecular masses were 7.7-9.2 kDa according to gel-filtration and mass spectrometry. Amino acid analysis revealed a high content of glutamic acid and valine and a low content of isoleucine, aromatic and sulfur-containing amino acids. Data illustrating the temperature and the pH stability of the inhibitors are presented. Each of the inhibitors formed a inhibitor complex with trypsin in a molar ratio 1:1 and contained an Arg residue at the reactive site. In addition to trypsin, BWI-1 and BWI-2 inhibited chymotrypsin, however, less effectively. None of the isolated inhibitors suppressed activity of papain, leukocyte elastase, pepsin and subtilisin.