Pediatric nurses are exposed to occupational stress due to the demanding care of sick children and complex interactions with families. The negative impact on nurse's physical and mental health, stress can also affect the quality of care. On the other hand, work engagement as a positive mental state and psychological capital as one of the supporting factors can help improve conditions and reduce occupational stress. However, the role of psychological capital in the relationship between occupational stress and work engagement in pediatric nurses needs further research. The aim of this study was to determine the mediating role of psychological capital in the relationship between work engagement and occupational stress in nurses working on pediatric wards. The present study was a predictive correlational study using the path analysis model. The statistical population of this study consisted of 251 pediatric nurses. The sampling was conducted from December 2023 to May 2024. Data collection instruments included the Demographic Profile Form, Chen's occupational Stress Questionnaire, Schaufeli et al.'s Work Engagement Questionnaire, and Luthans' Psychological Capital Questionnaire. The data analysis was carried out using the SPSS 26 and AMOS 24 software. The results of this study showed that there was an inverse and significant relationship between work engagement and occupational stress in nurses working in the pediatric ward (p <
0.001, β = -0.22). In addition, a positive and significant relationship was observed between work engagement and psychological capital among nurses (p <
0.001, β = 0.39). The results also showed that there was an inverse and significant relationship between psychological capital and occupational stress (p <
0.001, β = -0.23). The results of the final model represented psychological capital as a mediating variable that explains the relationship between work engagement and occupational stress of nurses. The results of this study showed that higher work engagement leads to a reduction in occupational stress in nurses working in the pediatric ward and that psychological capital acts as a mediating variable in this relationship. Nurses who have higher work engagement and psychological capital, experience less occupational stress. Age and work experience were also related to reduced stress and increased work engagement and psychological capital. It is suggested that hospital managers focus on educational and supportive programs to enhance psychological capital and increase the work engagement of nurses working in pediatric wards to improve the quality of care for children.