Theoretical background: Social anxiety during adolescence is often linked to deficits in emotion regulation, which can contribute to heightened negative affect and diminished positive affect in everyday life. Objective: This study investigated whether three emotion-regulation strategies – acceptance, suppression, and rumination – mediate the relationship between social anxiety and daily affect in adolescents. Method: A sample of 47 adolescents completed ecological momentary assessments over 14 days. Social anxiety was assessed as a trait, while daily positive and negative affect as well as emotion regulation strategies were measured multiple times per day. Results: Multilevel structural equation models showed that social anxiety was significantly associated with lower acceptance of positive and negative emotions, higher suppression of negative emotions, and increased rumination. Acceptance of positive emotions mediated the link between social anxiety and reduced positive affect, while rumination mediated the link with negative affect. Discussion and conclusion: These findings underscore the importance of addressing both positive and negative emotional experiences and their regulation in the field of social anxiety in adolescents.