Bronchogenic cyst is an uncommon congenital lesion which is derived from the primitive foregut. Most bronchogenic cyst may develope at the tracheal bifurcation, both main bronchi, the lung parenchymeand the mediastinum. A 40-year old male was evaluated for dyspnea and chest tightness. Computed tomography revealed a well dermarcated, 7.2 ${ imes}$ 7.9 cm sized, homogeneous mass compressing the left atrium. 2D-echo showed grade III mitral regurgitation. We completely removed the cystic mass and then confirmed the bronchogenic cyst in the pathological diagnosis. During the follow up period, the patient progressed well without any symptoms and showed grade I mitral regurgitation on the 2D-Echo. Therefore, we report a case of the bronchogenic cyst causing grade III mitral regurgitation.