BackgroundPsychiatric nurses routinely operate in high-stress, high-risk environments, making insomnia a prevalent issue that profoundly impacts their physical and mental well-being, as well as the quality of patient care. Empirical evidence suggests that insomnia not only diminishes occupational performance but also substantially increases the risk, posing a substantial risk to patient safety. Nevertheless, investigations into the underlying mechanisms driving insomnia among psychiatric nurses remain scarce.ObjectivesThis study aims to explore the relationship between perceived organizational support and insomnia in psychiatric nurses, as well as to examine the mediating role of psychological capital through the development of a mediation model. The findings are intended to provide novel insights for hospital administrators in addressing insomnia among nursing staff.MethodsA convenience sampling method was used to recruit 475 psychiatric nurses from three tertiary-level psychiatric specialty hospitals in Beijing. Data were collected between March and June 2024 using a general information questionnaire, the Perceived Organizational Support Scale (POSS), the Psychological Capital Questionnaire (PCQ), and the Athens Insomnia Scale (AIS). Statistical analyses included assessments for common method bias, descriptive statistics, one-way analysis of variance (ANOVA), independent samples t-tests, Pearson correlation analysis, and mediation analysis using Model 4 of Hayes' PROCESS macro.Results(1) Of the 475 psychiatric nurses, 395 (83.16%) were identified as experiencing insomnia. (2) The mean scores for perceived organizational support, psychological capital, and insomnia symptoms were 39.11 +/- 10.60, 106.35 +/- 14.38, and 11.88 +/- 5.55, respectively. (3) Perceived organizational support among nurses was positively correlated with psychological capital (r = 0.641, P < 0.001) and negatively correlated with insomnia (r = -0.348, P < 0.001). Additionally, psychological capital was negatively correlated with insomnia (r = -0.369, P < 0.001). (4) Mediation analysis revealed that the total effect of organizational support on insomnia was - 0.335. The direct effect was - 0.191, accounting for 57.01%, and the indirect effect via psychological capital was - 0.144, accounting for 42.99% of the total effect.ConclusionThe prevalence of insomnia symptoms among psychiatric nurses is notably high, and perceived organizational support serves as a negative predictor of insomnia. Additionally, psychological capital partially mediates the relationship between organizational support and insomnia among nurses. These findings suggest that clinical nursing managers may alleviate insomnia in psychiatric nurses by implementing concrete interventions, such as enhancing organizational support through structured programs, and fostering psychological capital via targeted development initiatives and resilience training.Clinical trial numberNot applicable.