Objective To explore the mediating effect of basic psychological needs on the relationship between peer support and organizational citizenship behavior in junior nurses and to provide a basis for nursing managers to take targeted measures to promote the organizational citizenship behavior of junior nurses, thereby enhancing the quality of nursing services and the overall performance of the organization.Methods A total of 550 nurses from four tertiary general hospitals in Henan province were selected using convenience sampling method.They were investigated with general information questionnaire, the Organizational Citizenship Behavior Scale, the Peer Support Scale (PSS) and the Basic Psychological Needs Scale.The structural equation modeling was used to analyze the mediating effect of basic psychological needs on the relationship between peer support and organizational citizenship behavior.Results A total of 524 questionnaires were finally included.Peer support score was 74.44±22.00, basic psychological need score was 32.28±6.25, and organizational citizenship behavior score was 89.60±10.17.Peer support was negatively correlated with basic psychological needs and organizational citizenship behavior, respectively (both P＜0.05), and basic psychological need was positively correlated with organizational citizenship behavior (P＜0.05).Hierachical regression analysis revealed that after controlling for general information variables, peer support and basic psychological needs explained 31.4% of the total variance in organizational citizenship behavior.Basic psychological need mediated the relationship between peer support and organizational citizenship behavior, with the mediating effect accounting for 36.045% of the total effect.Conclusion Nursing managers should pay attention to the role of peer support among junior nurses and satisfy their basic psychological needs, so as to promote junior nurses′ organizational citizenship behavior.