Previous research suggests that social anxiety symptoms are maintained and intensified by inflexible emotion regulation (ER). Therefore, we examined whether trait-level social anxiety moderates ER flexibility operationalised at both between-person (covariation between variability in emotional intensity and variability in strategy use across occasions) and within-person (associations between emotional intensity and strategy use on a given day) levels. In a sample of healthy college-aged adults (N = 185, Mage = 21.89), we examined overall and emotion-specific intensities (shame, guilt, anxiety, anger, sadness) (...) and regulatory strategies (i.e. experiential avoidance, expressive suppression, and rumination) in response to each day’s most emotionally intense event over 6 days. During the study period, we found a positive association between variability in emotional intensity and variability of experiential avoidance in individuals with lower, rather than higher, levels of trait social anxiety after controlling for key covariates (i.e. gender, personality traits, and stress exposure). However, we did not find evidence for the moderating role of trait social anxiety in ER flexibility assessed at within-person levels. Our findings highlight the need to delineate dynamic ER flexibility across everyday events. (shrink)