This study aimed to examine the mechanisms responsible for the association between the broad autism phenotype and depressive symptoms in mothers of a child with autism spectrum disorder. A total of 98 mothers who had a child with autism spectrum disorder between the ages of 2 and 16 years completed assessments of maternal broad autism phenotype, child behavior problems, romantic relationship satisfaction, friend support, family support, and maternal depressive symptoms. Results indicated that only romantic relationship satisfaction was a significant mediator of the relationship between maternal broad autism phenotype social abnormalities and maternal depressive symptoms, where greater broad autism phenotype social abnormalities were associated with lower relationship satisfaction, which in turn was associated with increased depressive symptoms. Child behavior problems were directly related to increased depressive symptoms. Implications regarding maternal mental health outcomes within this population as well as intervention implications are discussed.