Purpose : To evaluate criteria for differentiating benign versus malignant solitary pulmonary nodules (SPNs)by analyzing their morphology and perinodular parenchymal changes on CT/HRCT. Materials and Methods : Weretrospectively reviewed the CT/HRCT in 99 patients with SPN. Sixty two cases were proved by surgery, PCNA,clinical follow up and etc. Thirty seven cases were diagnosed by typical benign calcitication. We defined SPN as adiscrete, single lesion in the lung with margins that are sparp enough to permit measurement of diameter. Weexcluded lesions more than 4 cm in diameter and lesions with cavity from our study protocol. The study included 41malignant nodules and 58 benign nodules. Results : Mean diameter of malignant nodule was 2.9cm, benign nodule was2.2cm. Peripheral location of nodule was 28 in malignant nodules, 50 in benign nodules. Typical benigncalcification was observed in 37 tuberculoma and three hamartoma. Lobulated margin was noted in 32 malignantnodules and 14 benign nodules. Spiculated margin was observed in 17 malignant nodules and 20 benign nodules. Lowattenuation within the nodule was observed in 14 malignant nodules and 12 benign nodules. Pleural tail wasobserved in 14 malignant nodules and 31 benign nodules. Air bronchogram was noted in 18 malignant nodules and 4benign nodules. Juxta nodular tuberculosis was observed in 6 malignant nodules and 29 benign nodules. Conclusion :Malignant nodules were larger than benign nodules and more commonly demonstrated a lobulated contour and airbronchogram (p＜0.05). Benign dodules more commonly demonstrated low density in the nodule and associated withjuxta nodular tyberculosis and peripheral location (p＜0.05). Spiculatd margin and pleural tail were not helpfulto differentiate benign form malignant nodule.