This study begins with Budnick et al.'s (2020) argument that fear of missing out (FoMO), which has traditionally been treated as a negative interpersonal variable, can have both negative and positive effects in the workplace context(workplace FoMO). The purpose of this study is, first, to empirically confirm the ambivalent impact of workplace FoMO through its negative impact on job burnout and its positive impact on self-improvement. Second, we examine the differential role of two subtypes of work-related rumination, emotional rumination and problem-solving pondering, in the development of the ambivalent effects of workplace FoMO. The results showed that, first, higher workplace FoMO was associated with higher levels of both job burnout and self-improvement, confirming Budnick et al.'s (2020) ambivalent impact of workplace FoMO. Second, in the process of ambivalent effects of workplace FoMO on burnout and self-improvement, emotional rumination increased burnout in employees, while problem-solving pondering decreased emotional rumination and increased self-improvement. The academic implication of this study is that it empirically confirms the ambivalent effects and mechanisms of workplace FoMO, and the practical implication is that it shows that workplace FoMO can be linked to positive outcomes by paying attention to employees' workplace FoMO and supporting their self-improvement at the organizational level.