Purpose: This study aimed to identify the mediating effects of team trust on the relationship between the authentic leadership of the nursing unit manager as perceived by the nurses and the nurses’ organizational citizenship behavior (OCB). Methods: Data were collected from 276 nurses working over six months at a university hospital. The research model was designed based on the PROCESS Macro model 4 and analyzed using the SPSS 26.0 program. Results: The results show that authentic leadership and team trust had strong correlations with nurses’ organizational citizenship behavior. Nursing unit managers’ authentic leadership had a direct effect on team trust and organizational citizenship behavior. Team trust had a direct effect on organizational citizenship behavior. There was a mediation effect of team trust between authentic leadership and the organizational citizenship behavior of nurses. Conclusion To increase team trust in nursing units, the institution should provide systematic support such as education and training program to enhance the authentic leadership of nursing unit managers.