This study was conducted to certify the effect of aqueous extracts from fifty medicinal plants on the activities of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) in vitro. Each aqueous extract was prepared by combining one-part medicinal plants with twenty-parts distilled water at 80°C for 8 h. Among the fifty medicinal plants, Allium sativum L. and Cinnamomum cassia Presl were regarded as an effective anti-hangover substance. Allium sativum L. extract increased ALDH activity more than 2 times compared with ADH activity, enhancing the acetaldehyde degradation. Cinnamomum cassia Presl extract dramatically inhibited ADH activity compared with ALDH activity, thus potently decreasing the acetaldehyde formation. ADH and ALDH activities were proportionally inhibited according to the increased concentration of Cinnamomum cassia Presl extract. The aqueous extract of Cinnamomum cassia Presl at a concentration of 45.33 μg/mL inhibited ADH activity by 52.8% and ALDH activity by 11.0%.