Isolated bronchogenic cysts of the diaphragm are rare abnormalities. They are usually asymptomatic unless secondarily infected or large enough to cause compression of vital structures. The patient was a 31-year-old man and had no symptoms except mild postprandial epigastric discomfort. The chest X-ray and chest C-T examination revealed a mediastinal mass at the left cardio-vertebro-phrenic angle. We performed the operation under the impression of solid mass at mediastinum. We revealed that the mass was bronchogenic cyst in diaphragm. Therefore we report this case with review of literatures.