The experimental verification of the method of study of the primary specificity of the proteolytic enzymes by statistical analysis of the masses of proteolysis products of protein substrates using proteases with the known substrate specificity (glutamyl endopeptidase and trypsin) has been performed. The proposed method does not require direct determination of the amino acid sequence of the proteolysis products, reliably determines proteases with the narrow substrate specificity, and is relatively tolerant offor the presence of peaks of foreign impurities in MALDI mass spectra of the proteolysis products. It has been shown that for exclusion of the false positive results it is necessary to use a set of protein substrates with the subsequent averaging of the obtained statistical data.