This case report describes the diagnosis of secondary malignant lymphoedema in two dogs that had undergone a mastectomy. A remarkable severe oedematous lesion associated with lameness in the right hindlimb was observed in both cases. Diagnostic imaging examinations, including direct pedal lymphangiography (case 1) and lymphoscintigraphy (case 2), showed obstruction of lymph flow in the lymphatics of the right hindlimbs. Although the recommended medical management and physiotherapy had been applied to resolve the problems, oedema did not improve in the damaged region in both cases. Results of histopathological examinations suggested that the cause of the obstructed lymph flow was neoplastic cells in the lymphatics of the right hindlimb in both dogs.