PURPOSE: To provide a new compd. which consists of N-iodopropargyl hydantoin, which has antimicrobial activity and which is safe for animals and human bodies and used for an antimicrobial agent or the like to protect woods, coatings. fibers, leather or the like from attacks of microbes.

CONSTITUTION: This N-iodopropargyl hydantoin compd. having antimicrobial activity expressed by formula V or VI is obtd. by reacting a compd. expressed by formula I or formula II (e.g. 5,5-dimethylhydantoin) with propargylbromide in a solvent in the presence of a base by heating for propargylation to obtain a compd. expressed by formula III or IV (e.g. 3-(2-propynyl)-5,5-dimethyl hydantoin or the like), then adding N-iodosuccinimlde and dry acetone to prepare a uniform soln., and further adding silver nitrate to react at room temp. In formula I, A is 1-12C alkyl, benzyl, (substd.) phenyl or the like; R1, R2 are H, 1-3C alkyl, (substd.)phenyl or the like. In formula III, R3, R4 are H, 1-3C alkyl.