||A novel lysozyme inhibitor, hen egg white lysozyme inhibitor (Hewli) was isolated from the culture broth of a bacterium (strain I-139) identified as Bacillus subtilis. Maximum lysozyme inhibitory activity was obtained when the bacterium was grown aerobically in a medium consisting of 0.65 % glucose, 0.5 % sodium glutamate, 1% meat extract, and 4% Polypepton (pH 7.0), at 30°C after 30 to 35hr. Hewli was purified 69-fold from the culture supernatant of B. subtilis I-139 by ammonium sulfate fractionation, DEAE-Sephadex A-50 column chromatography, Sephacryl S-200 gel chromatography, DEAE-Toyopearl 650M column chromatography, affinity chromatography on a column of immobilized egg white lysozyme, and acetone extraction. The purified lysozyme inhibitor has an amino acid composition of aspartic acid, glutamic acid, valine, and leucine in a 1:1:1:4 molar ratio and fatty acid composition of palmitic acid and/or vaccenic acid. Hewli inhibited B. subtilis I-139 gh canase and animal lysozymes such as the hen, turkey, or human enzymes.