There is a long history examining the antecedents of maladaptive parenting practices. Indeed, in both the developmental and clinical literature, maternal anxiety has been linked to maladaptive parenting behavior, including engaging in high levels of control during mother–child interactions. However, the association between anxiety and controlling parenting is not consistent throughout the literature. Therefore, we sought to examine potential moderators that may impact the relation between anxiety and parenting. Specifically, we investigated maternal physiological regulation as a moderator of the relations between mothers’ characteristics of shyness–anxiety and their engagement in supportive parenting, restrictive parenting, and overprotective parenting. Sixty-six mothers of preschool-aged children participated. Mothers completed a questionnaire about their shyness–anxiety, and their respiratory sinus arrhythmia (RSA) was measured at baseline as an index of parasympathetic regulation. In addition, mothers completed the Childrearing Practices Q-Sort as an index of parenting. Analyses revealed that mothers’ shyness–anxiety was positively predictive of overprotective parenting and negatively predictive of supportive parenting. In addition, RSA moderated the relation between mothers’ shyness–anxiety and overprotective parenting, but not supportive or restrictive parenting. Results are discussed with regard to the significant role that maternal emotion regulation plays in parenting practices. Specifically, it appears that shy–anxious mothers’ emotion regulation may be an important area of focus for parent-training programs designed to prevent children’s anxiety.