Hepatic hydrothorax is defined as pleural effusion in a patient with cirrhosis of the liver and no cardiopulmonary disease. We reported a case of hepatic hydrothorax diagnosed by color Doppler ultrasonography. A 75-year-old woman with nonBnonC cirrhosis was admitted to our institution with right hydrothorax. Color Doppler ultrasonography revealed movement of fluid from the peritoneal cavity to the pleural space through a small diaphragmatic defect as a jet flow. The size of the diaphragmatic defect and the velocity of the jet flow changed in relation to the clinical course. Color Doppler ultrasonography proved to be useful for diagnosing hepatic hydrothorax.