Mothers of children with autism spectrum disorder (n = 70) completed online measures of global constructs (i.e., stable individual characteristics measured at time 1), which included resilience, depressive symptoms, and family functioning, followed by 14 daily questionnaires assessing relationship quality and affect on a given day. The global constructs were examined as predictors of daily relationship quality using multilevel modeling. Daily affect was examined in association with daily relationship factors (partner conflict, support from partner, and relationship happiness). Depressive symptoms and family flexibility predicted daily relationship quality. On a daily level, affect was associated with relationship quality. Results emphasize the potential of interventions to improve the quality of parents' relationships by addressing maternal mental health, family functioning, and daily affect.