Abstract: Objective To investigate the follow-up CT fndings of pulmonary neop lasm s after treatment with radiofrequency ablation (RFA) and im prove the value of CT in estimating the eff cacy of RFA in treatment of malignant lung tumor． Methods Thirty-four pulmonary neop lasm s in 28 patients adm itted to our hospital from M arch 2008 to December 2011 underw ent percutaneous CT-guided RFA． Tw enty-one neoplasms in 20 patients were primary lung cancer and 13 tumors in 8 patients were metastases． The mean pretreatment tumor maximal diameter was 3．6 cm (range, 1．5-5．0 cm)． A ll patients underwent follow-up contrast-enhanced helical CT scan immediately, 1, 3, 6 months later, and then every 6 months, after undergoing RFA． Patients were divided into two groups, the com plete ablation group (Group A) and the incomp lete ablation or recurrence group (Group B)． The serial CT appearance and its evolution were assessed on follow-up CT． Results The main CT findings of Group A were as follow s: 1．The tumor density decreased generally with a blurred boundary and an enveloped ground-glass opacity surrounding tumor, and no enhancement show ed on immediate post-treatment CT． 2． The ablated area appeared as a demarcated oval homogeneous unenhanced solid lesion on the CT obtained 1-3 months after treatment． The lesion size might become slightly larger compared with pre-treatment． 3． From 3 to 6 months after treatment, the lesion size decreased variably without or with slight periphery enhancement． 4． The treated lesion size gradually decreased after the 6-month follow-up CT examination and generally show ed as an irregular line or strip seldom with slight enhancement． In Group B, there were no typical fndings indicating whether the tumor was incom plete ablation com pared with that of the com plete ablation on the early follow-up CT scans． How ever, 3 months later, the ablated lesions gradually increased or grew again after previous shrank with various degrees of inhomogeneous enhancement． Conclusion The gradual decrease of lesion size with or without slight homogeneous enhancement on beyond 6-month follow-up CT examination indicates the com plete ablation．On the contrary, the gradual increase or enlarging again follow ing the previous decrease with strong inhomogeneous enhancement imp lies the incom plete ablation or recurrence．