NOVELTY - Preparing a biodegradable antimicrobial agent, comprises: (a) forming an aqueous polypeptide solution by dissolving a polypeptide into an aqueous solution (10); (b) providing an aqueous sodium hypochlorite solution (12); (c) adding the aqueous sodium hypochlorite solution into the aqueous polypeptide solution to form a mixture (14); and (d) mixing the mixture for at least 1 minute such that the polypeptide compound reacts with sodium hypochlorite in the aqueous sodium hypochlorite solution (16), thus forming a polypeptide chloride having at least one N-halamine group.    USE - The method is useful for preparing antimicrobial agent (claimed), which is used against bacteria including gram-positive and gram-negative bacteria, fungi, molds and viruses. The antimicrobial activity of antimicrobial agent was tested against Escherichia coli using quantitative antimicrobial test according to the antimicrobial standards of ASTM E2149 under dynamic contact conditions. The results showed that polyglutamic acid chloride exhibited greater than 99.9% of antibacterial activity after 24 hours of treatment.    ADVANTAGE - The method: eliminates the need of time consuming chemical synthesis requiring organic solvent; and provides high yield of antimicrobial agents having high water-solubility, high sterilization efficiency and long duration, reduced harm to environment due to low toxicity, high biocompatibility, regenerative antimicrobial capability, and easy preparation with low cost.    DETAILED DESCRIPTION - Preparing a biodegradable antimicrobial agent, comprises: (a) forming an aqueous polypeptide solution by dissolving a polypeptide into an aqueous solution; (b) providing an aqueous sodium hypochlorite solution; (c) adding the aqueous sodium hypochlorite solution into the aqueous polypeptide solution to form a mixture; and (d) mixing the mixture for at least 1 minute such that the polypeptide compound reacts with sodium hypochlorite in the aqueous sodium hypochlorite solution, thus forming a polypeptide chloride having at least one N-halamine group, where the polypeptide compound is a polyglutamic acid or polyaspartic acid, and the polypeptide chloride is a polyglutamic acid chloride or polyaspartic acid chloride.    DESCRIPTION OF DRAWING(S) - The figure shows a process flow diagram of preparing biodegradable antimicrobial agent.    Forming an aqueous polypeptide solution (10)    Providing an aqueous sodium hypochlorite solution (12)    Adding the aqueous sodium hypochlorite solution into the aqueous polypeptide solution to form a mixture (14)    Mixing and reacting the mixture (16)