Objective: To assess the therapeutic effects of radio frequency ablation (RFA) in the treatment of patients with unresectable malignant lung tumors. Methods: Twenty patients with primary or metastatic malignant lung tumors received RFA treatment, and imaging analysis with CT, X-ray and position emission tomograghy (PET) was performed 1 week before and 1 to 2 weeks after treatment Results and Conclusion: Postoperative fever occurred in 6 patients and pneumatothorax during the RFA procedures was found in 5 patients. PET demonstrated that tumors smaller than 3.5 cm in diameter, which is the general coverage of the RFA system we adopted, dissipated after RFA, and the proportion of the larger tumors within RFA coverage was destroyed, while the rest outside remained intact. PET is currently the most reliable technique to observe the short-term therapeutic effects of RFA on tumors in comparison with other imaging approaches.