This review summarizes data on the properties of L-lysine alpha-oxidase, an enzyme that belongs to the group of oxidases of L-amino acids. This enzyme acts virtually only on L-lysine with a rather low Km yielding alpha-keto-epsilon-aminocaproic acid. The decrease in the level of the essential amino acid L-lysine and the formation of hydrogen peroxide during the reaction possibly provide the basis for the unique properties of L-lysine alpha-oxidase: cytotoxic, antitumor, antimetastatic, antiinvasive, antibacterial, and antiviral activities, as well as an immunomodulating effect. Native L-lysine alpha-oxidase and its immobilized forms are promising tools for determination of concentration of L-lysine in various biological materials.