The present invention provides a composition for removing a hangover. In particular, the present invention discloses a method of using ajoene as an alcohol dehydrogenase inhibitor based on the fact that ajoene strongly inhibits alcohol dehydrogenase (ADH) activity. A composition for removing a hangover comprising ajoene suppresses the over-production of acetaldehyde during alcohol metabolism to maintain acetaldehyde concentration in blood at a normal level that can be degraded in the body and eliminated therefrom through normal metabolic and secretory pathways to thereby prevent the hangover after consumption of alcohol, and a method of preparing the same, are also provided. The present invention also provides a novel use of ajoene, which is a natural substance obtained by purification of garlic, and a composition for removing a hangover comprising ajoene, which is harmless to the body and strongly inhibits ADH activity, thereby showing very excellent relieving effect on the hangover.