Frontline staff plays an essential role in the survival of a service company. Among the demands of their job, experiencing customer mistreatment is inevitable in their daily work. This study examines the impact of customer mistreatment (CM) on frontline employees' (FLEs) extra-role performance and turnover intention via the mediating role of rumination. Through a sample of 200 frontline staff working in the airport, the partial least squares structural equation modelling (PLS-SEM) was used to analyze the data. The finding reveals that CM directly impacts employee turnover intention and indirectly affects employees' extra-role performance via rumination. Although much research has investigated the antecedents that predict employees' turnover intention and extra-role performance, little is known about the underlying mechanism in the link between CM – employees' extra-role performance and turnover intention. This study thus fills the gaps in the literature. Implications for theory, practice, and future research are discussed.