BackgroundAn increasing number of empirical studies on medical professionalism in clinical practice settings have been conducted since 2002. However, few of them were carried out in China, and few focused on the influence of department climate on clinical physicians' professionalism. Our study investigated Chinese clinical physicians' professional attitudes and behaviours, and evaluated the effect of department climate on their attitudes and behaviours. MethodsSelf-administered questionnaires including 20 items on professional attitude, ten items on behaviour, and 29 items on department climate were distributed to clinical physicians in four public hospitals in non-capital cities in Sichuan and Hubei Provinces, China, from Nov 29 to Dec 7, 2016. Verbal informed consent was obtained from the participants. Findings327 valid questionnaires were collected. More than 305 (94%) respondents agreed with 13 of 20 specific statements on medical professionalism. 125 (38%) respondents disagreed with reporting incompetent colleagues, 113 (35%) disagreed with recertification, and 98 (30%) disagreed with reporting medical errors. More than 294 (90%) respondents reported that they sometimes, usually, or always manifested the four positive behaviours on the questionnaire, and more than 261 (80%) reported that they never displayed the six negative behaviours. Factor analysis indicated that the department climate scale (26 items) consists of six dimensions. Regression analyses indicated that the predictors of professional attitudes were two dimensions of climate scale (serving patients [β 0·325, 95% CI 0·153–0·307] and work support [0·170, 0·036–0·161]; adjusted r2 0·174). Physicians' behaviour was significantly influenced by one dimension of climate scale (serving patients; β 0·280, 95% CI 0·112–0·254), professional attitude (0·182, 0·067–0·269), and educational background (Master's degree [0·244, 0·076–0·305] and Bachelor's degree and above [0·193, 0·032–0·238; comparison group is below Bachelor's degree]; adjusted r2 0·169). InterpretationPhysicians showed relatively positive professional attitudes and behaviours. Department climate (especially the dimension of serving patients) affected physicians' attitudes and behaviours, suggesting that improvement of department climate in the hospital is an important strategy to enhance professionalism. FundingNational Natural Science Foundation of China (71203069, 71573094), the Fundamental Research Funds for the Central Universities, HUST (2013WZ024, 2015AC027).