A 75-year-old man underwent esophagectomy for thoracic esophageal cancer. After the operation, the output fluid from the right chest drain increased, and laboratory analysis confirmed the fluid to be chyle. Magnetic resonance imaging (MRI) was then carried out to identify the leakage point and the size of the injury to the thoracic duct. The MRI clearly showed the leak point to be in the lower thoracic region. It thus appears that this non-invasive new approach using MRI is effective and suitable for diagnosis and establishment of an appropriate treatment plan for chylothorax after thoracic surgery.