Cardiac leiomyosarcoma is an extremely rare tumor with a poor prognosis. We reported an 18- year-old girl with a left atrial leiomyosarcoma extending to right lower pulmonary veins. We performed complete tumor excision by the right anterolateral mini-thoracotomy approach using minimally invasive techniques. After pathological confirmation of the tumor, right lower lobectomy was performed with the same incision one week later to prevent a recurrence. Although no tumor remnant was found in the lobectomy specimen, adjuvant chemotherapy was started. No recurrence was detected during the 12-month follow-up.