The glucocorticoid receptor gene NR3C1 is an important down-regulator of inflammation and is typically under-expressed in individuals with low socioeconomic status (SES). Negative emotionality has been suggested as a potential mediator of SES disparities in health outcomes. In this study, we expand this literature by naturalistically assessing negative emotionality in a key emotional environment: the family. In a sample of 104 youth with asthma (10-17 years) and their primary caregiver, we assessed SES via caregiver report, emotional expression by youth and parents in the home over four days using the electronically activated recorder (EAR), and NR3C1 expression via blood collected from youth. Although there was not a direct effect of SES on NR3C1 expression, bootstrapping mediation analyses showed a significant indirect path such that lower SES was associated with a more negative family emotional climate, which in turn predicted reduced NR3C1 expression. No mediation effects were found for family positive emotional climate. This research demonstrates the importance of examining the effects of SES on emotion expression in the family context and suggests a critical biopsychosocial pathway underlying SES-based health disparities that may extend beyond youth.