We perform radiofrequency interstitial thermal ablation (RFA) using a new device for unresectable liver tumors, and evaluate its efficacy and safety. This study Involved a total of 136 liver tumors in 40 patients (including 13 patients with hepatomas and 27 patients with metastases). The size of tumors ranged from 5mm to 126mm. Under ultrasound guidance an electrode cannula was introduced into the tumor, which was then thermally ablated at 80°C to 120°C under ultrasound imaging monitoring, using a RFA device at the frequency of 460kHz. The efficacy of this RFA therapy was evaluated by perioperative and follow-up CT scans and tumor markers. The average follow-up period was 8.5 months. The approaches to the tumors were percutaneous in 18 patients, laparoscopic in four patients and open surgical in 18 patients. The RFA effectively ablated in 127 out of 136 tumors (93.3%). Complications included a skin burn at the grounding pad in one patient, pleural effusion in three patients, ascites in four patients and mild heart failure in one patient; however, there was no serious morbidity such as bleeding and infection. The survival rates at the time up to 20 months were 85.7% for patients with hepatomas and 88.2% for patients with metastases. The present study has demonstrated that the RFA is able to provide a safe and effective means in controlling liver tumors. The long-term study of more patients treated by RFA is warranted.