Abstract: Objective The purpose of this study is to find out the effective way to define bronchioloalveolar carcinoma and decrease the incorrect diagnosis. Methods The clinical and radiological features were analyzed retrospectively in 132 cases of the proven BAC and 30 cases with pneumonia.The different clinical and radiologic features between BAC and pneumonia were evaluated through the score forms. Results The following features were significant in BAC group，including no symptom or physical sign in respiratory system，dry cough，cough with white mucous sputum，ground-glass opacity(GGO) with partly solid and radiolucencies，solid nodules or masses with irregular margin，consolidation with air-filled bronchi，the consolidation with nodules.The following features were significant in pneumonia group，including fever，cough with purulent sputum，bubble rales in the lung auscultation，increased WBC，pure GGO，nodule or mass with regular margin，and consolidation without air-filled bronchi (P<0.05).If these features were selected as the index to direct BAC or the pneumonia，and 1 or -1 as the score of every feature，and computed the total score to diagnose BAC.It was a significantly effective method and the area of ROC curve was 0.980（P=0.000），asymptotic 95% confidence interval was 0.959 and 1.001. The sensitivity and specificity for diagnosing BAC were 90.9% and 93.3% respectively. Conclusion There were some different clinical and radiological features between BAC and pneumonia，and it was an easy and effective method to diagnose BAC by combining these features.