A one-year old castrated Ragdoll cat with previously diagnosed hypertrophic cardiomyopathy by echocardiography was visited for dyspnea and depression. With survey radiography and the analysis of pleural effusion, chylothorax was diagnosed. To further evaluate the cause of the chylothorax, lymphography by percutaneous iohexol injection into the popliteal lymph node was performed. Iohexol (Omnipaque 300; Carringtohill, GE, Cork, Ireland) was injected via popliteal lymph node under general anesthesia with ultrasonographic guidance. Computed tomography (CT) was performed immediately after contrast media injection. The thoracic duct was visualized on helical CT images. At the level of caudal thoracic cavity, single thoracic duct was observed. At the level of cranial mediastinum, thoracic duct was tortuous and focally dilated, and leakage of contrast medium was identified. In conclusion, thoracic duct imaging by percutaneous iohexol injection into popliteal lymph node was successful in a cat with secondary chylothorax with hypertrophic cardiomyopathy, and the present lymphographic method was considered clinically easy and reliable.