Purpose : We evaluated the usefulness of quantitative spiral CT to predict postoperative lung function inpatients undergoing pulmonary resection. Materials and Methods : Fourteen patients in whom pneumonectomy orsegmentectomy were performed underwent preoperative chest spiral CT and pulmonary function test(PFT). Six patientsunderwent postoperative follow-up PFT. Ten patients underwent preoperative radioisotope(RI) lung perfusion scan.Preoperative CT data were postprocessed with contiguous pixel method ranged from -910HU to -500HU to quantifytotal functional lung volume(TFLV) and regional volume to be resected(RFLV). Postoperative lung function waspredicted by following formula; Predicted postoperative PFT value = preoperative PFT x (1-RFLV/TFLV). CT predictedvalue was compared with postoperative measured PFT value and those value of RI perfusion scan. Results : CTpredicted values were very close to postoperative measured value and RI predicted value, and were correlated wellwith postoperative measured values (FVC: r=0.988, P<0.001; FEV1: r=0.994, P<0.001) and RI predicted values (FVC:r=0.976, P<0.001; FEV1: r=0.974, p<0.001). Conclusion : Quantitative spiral CT was useful to predict postoperativelung function and could be an effective alternative to RI perfusion scan.