Q fever is a zoonosis caused by Coxiella burnetii, presenting as acute and chronic illness and it has been reported worldwide. Acute Q fever is usually asymptomatic or mild and self-limiting, but infective endocarditis is one of the most serious complications of chronic Q fever and can be fatal. Known risk factors for Q fever endocarditis are valvular heart disease, immunocompromised hosts, and pregnancy. There have been some reports on Q fever in Korea but there exists no report on Q fever endocarditis. We have experienced 2 cases of Q fever with underlying valvular heart disease; both patients came to the hospital for evaluation of prolonged fever. Although Q fever and Q fever endocarditis are rare in Korea, Q fever endocarditis should be considered in the differential diagnosis of patient with infective endocarditis when causative microorganism cannot be identified.