<p>Adolescents face heightened vulnerability to depressive symptoms due to biological, psychological, and social transitions. Experiential avoidance (EA), a core component of psychological inflexibility, has been established as a transdiagnostic risk factor for internalizing problems. While self-reassurance and self-criticism are critical self-related processes influencing emotional resilience, their interactive roles with EA in adolescent depression remain underexplored, particularly in non-Western contexts. This study examined the interaction effects of EA with self-reassurance and self-criticism on depressive symptoms among Japanese adolescents. A short-term longitudinal study was conducted with 391 Japanese middle school students (aged 12–15). Depressive symptoms and EA were assessed at Time 1, while self-reassurance and self-criticism were measured at Time 2, eight months later. Hierarchical multiple regression analyses were performed to test whether EA interacts with these self-related processes in predicting later depressive symptoms. EA significantly predicted increases in depressive symptoms, even after controlling for baseline levels. Importantly, a significant interaction effect between EA and self-reassurance was found in predicting decreased activity and pleasure, a core dimension of adolescent depression. The adverse impact of EA was particularly pronounced among adolescents with lower self-reassurance. In contrast, no significant interaction was found between EA and self-criticism. These findings highlight the role of self-reassurance in interacting with EA to influence depressive outcomes. Enhancing self-reassurance may mitigate the detrimental effects of psychological inflexibility on adolescent mental health. The culturally nuanced function of self-criticism warrants further investigation.</p>