Self-esteem is a positive evaluation of oneself that can facilitate optimal functioning. However, little research has focused on its antecedents in sport. Accordingly, we adopted an interactionism perspective and proposed that gratitude, a dispositional factor, will enhance an athlete's self-esteem and affective trust in coach, a situational factor, will strengthen such a positive effect. Athletes completed measures of gratitude, affective trust in coach, and self-esteem at Time 1 and self-esteem at Time 2 after 6 months. Results showed that athletes with higher levels of gratitude increased their self-esteem over time when they had higher affective trust in their coaches.