To achieve complete ablation of liver cancer in the hepatic dome, thoracoscopy-assisted radiofrequency ablation was attempted in three patients. Under general anesthesia and left lateral position, a thoracoport site was placed in the 6th intercostal space and a small thoracotomy was placed in the 7th intercostal space. In all three cases, the liver cancer was located in the hepatic dome of segment 7/8 and the tumor could not be fully observed on the lung echogram. In Case 1, saline was infused into the thoracic cavity under thoracoscopic observation and percutaneous ablation was safely performed. In Cases 2 and 3, the right diaphragm was opened, guided by ultrasonography, and the electrode was inserted into this working space via the thoracotomy site. At day 7, complete ablation was confirmed by computed tomography. All patients recovered and were discharged after a short hospital stay without severe complications. Tumor recurrence has not been observed in any patient at this stage. For liver cancer located in the right subphrenic dome of the liver, thoracoscopy-assisted ablation is a safe and useful option particularly in patients with poor hepatic function.