PROBLEM TO BE SOLVED: To provide a flavor improver for improving the flavor of Miso or Miso-containing food and drink to further natural excellent flavor with natural feeling, and to provide a method for improving the flavor of Miso or Miso-containing food and drink, using the improver.SOLUTION: This flavor improver composition of Miso or Miso-containing food and drink includes at least one flavor improver selected from the group consisting of 1-octene-3-one, (Z)-1,5-octadiene-3-one, and 4,5-epoxy-(E)-2-decenal as an active ingredient, and is packed or heat treated. The method for improving the flavor of the Miso or Miso-containing food and drink includes addition of 0.1 ppt-100 ppb of the flavor improver to the packed or heat treated Miso or Miso-containing food and drink.
