The present invention relates to a preservative efficacy-enhancing agent capable of allowing an antiseptic agent to exhibit a high preservative efficacy even when the antiseptic agent is used at a low concentration a preservative efficacy-enhancing composition containing the same and a method for enhancing a preservative efficacy of antiseptic agents. The present invention relates to: (1) a preservative efficacy-enhancing agent for antiseptic agents which includes an amphiphilic galactose derivative (A) as an effective ingredient (2) a preservative efficacy-enhancing composition including 0.01 to 30% by mass of an amphiphilic galactose derivative (A) and 0.01 to 1.0% by mass of an antiseptic agent (B) and (3) a method for enhancing a preservative efficacy of an antiseptic composition which includes the step of allowing 0.01 to 30% by mass of an amphiphilic galactose derivative (A) to coexist with an antiseptic agent (B) in the composition.
