Polylysine is a homopolymer of L-lysine, as a natural, toxicologically safe, antibacterial food preservative. It can inhibit the growth of bacteria, yeasts and moulds bacteria, especially inhibit the Gram(-) bacteria which can't easily inhibit by other preservatives, such as coli, Salmonella, and also can inhibit the thermophilics, such as bacillus-bacilli. Its activity is not affected by pH, and stable when heated. Therefore, it can be sterilized along with the raw material. It is a food preservative which is highly efficient, safe, and has no side-effects. It has lots of advantages over traditional preservatives, such as high safety good heat tolerance and solubility in water and extensive antimicrobial against Gram+ bacteria and fungi.