The present study investigated physiological synchrony across mothers, fathers, and adolescents during a conflict discussion. In particular, a multilevel, within-dyad approach was used to parameterize synchrony within the parasympathetic nervous system. Moreover, we examined how domains of conflict within the larger family system influenced the level of synchrony between family members. Participants were 191 families with adolescents (M age = 12.4 years), whose respiratory sinus arrhythmia (RSA) were measured during a triadic family conflict discussion. On the minute-to-minute basis, mothers and adolescents as well as mothers and fathers exhibited positive RSA concurrent synchrony, whereas no such concordance was observed between adolescents and fathers. In addition, the presence of conflict between parents with respect to coparenting moderated the level of mother-adolescent synchrony such that no concordant RSA synchrony emerged between mother and adolescents under high levels of coparenting conflict. In contrast, general interparental conflict did not moderate levels of physiological synchrony among any of the dyads. Findings suggest that mothers may be particularly physiologically in tune with family members in the context of conflict discussions and specific domains of family conflict may influence concordant physiological dynamics. Taken together, this is one of the first studies to examine physiological synchrony during the adolescent period and results suggest this may be an important developmental period for these dynamics. (PsycInfo Database Record (c) 2020 APA, all rights reserved).