Emotion regulation strategies can enhance teachers' well-being and performance by enabling them to cope with the challenges and stressors of teaching. Personality traits, however, may affect teachers' vulnerability to depression and their capacity to regulate their emotions. To investigate how emotion regulation strategies mediated the relationship between EFL teachers' personality traits and depression, we invited 546 Chinese EFL teachers to complete the relevant online questionnaires. The Structural Equation Modelling (SEM) results revealed that teachers' personality traits directly influenced their depression levels, and that their depression levels negatively impacted their emotion regulation strategies. Furthermore, the results demonstrated that positive emotions mediated the relationship between teachers' personality traits and depression, suggesting that teachers with higher levels of positive emotions had lower levels of depression and more effective emotion regulation strategies. The findings implied that fostering positive emotions and emotion regulation strategies can improve teachers' mental health and teaching quality. The study also added to the knowledge of the role of emotion regulation strategies in the interplay between personality traits and depression.