Parents, especially mothers, of a child with an Autism Spectrum Disorder (ASD) are more likely to experience higher levels of stress, and adaptive emotion regulation strategies, such as mindfulness and acceptance, may decrease stress among parents of children with ASD. Research has shown that mindfulness-based interventions reduce perceived stress among parents of typically developing children and improve the parent-child relationship, and similar interventions may be helpful for mothers of children with ASD. However, research has not yet established that mindfulness is related to decreased stress among parents. It is important to first establish this relationship, given the possibility that other factors, such as child behavioral difficulties or parental psychopathology are stronger predictors of maternal stress than the mother's regulation strategies. This study examined the unique contribution of maternal mindfulness to maternal stress in a sample of mothers (n = 154) who completed an online battery of measures. As predicted, maternal mindfulness significantly predicted level of maternal stress, above and beyond child behavior problems and maternal psychopathology, and this relationship was not moderated by child's ASD diagnosis. Maternal emotion regulation and effortful control were also significantly related to maternal stress, and may account for the explained variance of mindfulness. These findings and their implications are discussed.