Purpose This study aimed to determine the mediating effect of leader-member exchange (LMX) on the relationship between nursing unit managers’ethical leadership and nurses’turnover intentions. Methods A cross-sectional nationwide survey was performed using structured questionnaires. A total of 225 clinical nurses working in general tertiary hospitals were recruited through proportional quota sampling; the quota used represented the location of working hospitals in South Korea. Data were collected through an online survey and snowball sampling from June to September 2022 and analyzed using the SPSS 25.0 program. A mediation analysis was performed using a simple mediation model applying the PROCESS macro with 95% bias-corrected bootstrap confidence interval. Results In bootstrapping, the indirect effect (X→M→Y) was statistically significant (B=-0.77, 95% CI:-1.02 to -0.50). LMX showed a mediating effect on the relationship between nursing unit managers’ethical leadership and clinical nurses’ turnover intention. In this model, the total effect was B=-0.93 (p<.001). Conclusion These findings suggest that LMX must be considered when making a strategy for nursing retention in the hospital setting. Nursing unit managers with ethical leadership could decrease nurses’ turnover intention by improving the LMX.