The existing literature has yet to thoroughly explore how employees process leader negative feedback in the context of organizational climate. Drawing on social information processing theory, this study proposes and tests a model that clarifies how and when leader negative feedback enhances employee task proficiency. Based on two experiments and a multi-wave field study (Ntotal = 530), our findings show that leader negative feedback increases employees' mental preoccupation with work, which in turn enhances task proficiency. Furthermore, the perceived rule climate strengthens the mediating role of mental preoccupation with work in the relationship between leader negative feedback and task proficiency. These findings contribute to the theoretical understanding of the mechanisms and boundary conditions that shape employees' responses to leader negative feedback. This work offers practical insights for leaders on how to deliver negative feedback effectively, providing a robust theoretical foundation to inform organizational practices.