To obtain products having a particularly excellent antimicrobial property, mildew-proofing property, safety, liquid preservable and stable property, etc., by including at least an amphoteric surfactant and a flavonoid deriv. into the compsn.

The amphoteric surfactant of a glycine type is expressed by formula I. In the formula, R is a 6 to 16C alkyl, etc., and denotes an octyl group, dodecyl group, etc. The flavonoid deriv. is the compd. of the flavonoid expressed by formula II as a skeleton. The antimicrobial compsn. is obtd. by mixing at least the amphoteric surfactant and the flavonoids deriv. The antimicrobial compsn. prepd. by mixing the amphoteric surfactant at a ratio of about 0.5 to 30 pts.wt., more particularly 1 to 20 pts.wt. per 1 pt.wt. flavonoid deriv. is more preferable. The mixing method is preferably executed by mixing the aq. soln. of the flavonoid deriv. and the aq. soln. of the amphoteric surfactant. At this time, the flavonoid deriv. is preferably added to the aq. soln. of the amphoteric surfactant previously adjusted to pH5 to 7 at 25°C.