Research on authentic leadership has yielded important insights about its effects on subordinates. However, its consequences for the leaders themselves remain largely unexamined. This is problematic, as organizations require their leaders to provide guidance and leaders' mental well-being is a prerequisite for this. Drawing on the theories of ego-depletion and authentic leadership, we investigate the role of authentic leadership in predicting leaders' mental well-being. In an experience sampling study, we apply hierarchical linear modeling to analyze 396 observations from 44 executives. Our multilevel moderated mediation analyses reveal that authentic leadership reduces leaders' stress and increases their work engagement and that these effects are mediated by leader mental depletion. Moreover, we show that the indirect effects are contingent on the extent to which leaders interact with their subordinates: authentic leaders deplete less with increasing follower interaction, while inauthentic leaders deplete less with decreasing follower interaction.