Objective To investigate the effects of organizational support and organizational identification on professionalism among resident physicians and the underlying influence mechanisms, to suggest strategies to cultivate professionalism of resident physicians and facilitate the high-quality development of standardized residency training. Methods A questionnaire survey was conducted among resident physicians at a tertiary hospital in Beijing from August 2024 to June 2025. The survey instruments comprised of scales for organizational support, organizational identification, and professionalism. A structural equation model was established to analyze the pathways whereby organizational support and identification affect professionalism, and the bootstrap method was applied to examine the mediating effect of organizational identification. Results The average score of organizational support, organizational identification, and professionalism were (4.32±0.53), (4.29±0.56) and (4.55±0.46), respectively, among which pairwise correlations were found among organizational support, organizational identification, and professionalism (r=0.734-0.851, P<0.001). The results of the structural equation modeling analysis revealed that both organizational support (β=0.401) and organizational identification (β=0.486) had a significant positive impact on professionalism (all P<0.05). The mediation analysis indicated that organizational identification played a mediating role in the effect of organizational support on professionalism (indirect effect: 51.0%). Conclusions Resident physicians have a high level of organizational support, organizational identification and professionalism. Organizational identification plays a partial mediating role in the impact of organizational support on professionalism. Training bases are advised to promote professionalism training by enhancing organizational support to foster resident physicians' organizational identification.