Purpose: Liquid-based cytology have been developed and currently used to overcome the limitation of conventional cytology. This study aims to evaluate the differences between conventional cytology and ThinPrepⓇ in the bronchial washing. Materials and Methods: Both conventional cytology and ThinPrep Ⓡ were performed in the 2,551 cases of bronchial washing, of which, 116 cases of histologically diagnosed as lung cancer were evaluated. Results: Among the 116 cases, 23 and 4 cases were negative in conventional cytology and ThinPrepⓇ , respectively. The thirty eight cases in conventional cytology and 30 cases in ThinPrep Ⓡ were diagnosed as “atypical.” Malignant carcinoma was 54 cases and 82 cases in conventional cytology and ThinPrep Ⓡ , respectively. The positive predictive value, negative predictive value, sensitivity and specificity were 98.94%, 99.06%, 80.17%, and 99.96%, respectively in conventional cytology. Those were 99.12%, 99.83%, 96.55% and 99.96%, respectively in ThinPrepⓇ . Conclusion: ThinPrep Ⓡ (liquid-based cytology) revealed higher sensitivity and lower false negative rate than conventional cytology. ThinPrepⓇ has many advantages to diagnose the lung cancer from bronchial washing cytology. (J Lung Cancer 2012;11(2):84�� 88)