This report describes a hepatitis A outbreak among Korean military personnel. Each case of hepatitis A in this outbreak was defined as a person who had symptoms compatible with acute viral hepatitis A and had positive HAV IgM between May 2 and August 14, 2007 in Inje district, Gangwon, Korea. We tested 70 cases with symptoms for HAV IgM, and 67 cases showed positive results. They included 4 sergeants, 1 officer and 62 privates. A positive result for HAV IgG among asymptomatic military personnel was seen in 11.8% of cases. This epidemic occurred after a heavy rainfall in the military compound area where drinking water was supplied by the stream water. After the outbreak, the supply of drinking water was switched to a public water system. All of 178 military personnel who had no HAV IgG were vaccinated on July 26, 2007. The outbreak was resolved after the control measures were implemented.