The present invention relates to: a method for preparing a Hovenia dulcis Thunb fruit fermented vinegar having hangover relief and liver protection effects; and a beverage composition prepared using the same as a main ingredient. In the method for preparing fermented vinegar by using Hovenia dulcis Thunb fruits of the present invention, a Hovenia dulcis Thunb fruits concentrate is made using Hovenia dulcis Thunb fruits and is adjusted to 16 °Brix. 10% (v/v) seed mash is inoculated thereto and subjected to alcohol fermentation at a temperature of 28 to 32 °C. Then obtained alcoholic fermentation filtrate is used as a substrate of acetic acid fermentation. In the acetic acid fermentation, a fermented liquid obtained through alcoholic fermentation of Hovenia dulcis Thunb fruits is inoculated with 10% (v/v) of a vinegar starter, and then fermented at a temperature of 28 to 32 °C under a 120 to 180 rpm condition.