["Applied Psychology: Health and Well-Being, Volume 18, Issue 3, June 2026. ", "\nAbstract\nAlthough childhood trauma has been linked to loneliness in adolescents, the psychophysiological mechanisms that may underlie this association remain poorly understood. This study examined whether emotion dysregulation mediated the relation between childhood trauma and loneliness in adolescents, and whether parasympathetic functioning—indexed by baseline respiratory sinus arrhythmia (RSA) and RSA suppression to a social stress task—moderated the relation. Participants were 245 Chinese adolescents (Mage = 12.91 years, SDage = 0.69 years, 46.12% male). They completed self‐report questionnaires on childhood trauma, emotion dysregulation and loneliness. They also completed a public speech task designed to elicit social stress, during which their physiological data were collected. The results demonstrated that childhood trauma was positively related to adolescent loneliness, and emotion dysregulation partially mediated this relation. Moreover, parasympathetic functioning moderated the mediation model, such that the indirect association between childhood trauma and loneliness through emotion dysregulation was significant only among adolescents with lower baseline RSA and blunted social stress RSA suppression. The findings suggest that parasympathetic functioning as indicated by higher baseline RSA and greater RSA suppression in response to social stress may serve as risk‐buffering physiological markers, potentially ameliorating emotion dysregulation linked to childhood trauma, which in turn is associated with increased loneliness in adolescents.\n"]