Lysozyme was reacted with xylose, methyl linoleate, gly-oxal, methylglyoxal and diacetyl in an aqueous system (50°C, pH 6.0), and browning, polymerization, changes of amino acids composition and relative digestibility of the browned lysozyme were investigated. Browning intensity as well as degree of polymerization of lysozyme in the reaction with α-dicarbonyls was higher than with xylose or methyl linoleate. After 10 days of reaction with α-dicarbonyls, the amino acid composition of lysozyme was markedly affected; i.e., 30-70% of lysine, 40-50% of tryptophan and 90% of arginine were lost respectively. By digestion with a pepsin-pancreatin system, it was observed that the relative digestibility of lysozyme reacted with dicarbonyl was lower than that of lysozyme reacted with methyl linoleate or xylose.