This current study examined maternal characteristics that predict the use of overprotective parenting in mothers of toddlers. Maternal respiratory sinus arrhythmia (RSA) reactivity was tested as a moderator of the relation between maternal anxiety and overprotective parentig. Mothers (n = 151) and their 2-year-old toddlers participated in a laboratory visit and returned for a follow-up visit 1 year later. At child age 2, mothers reported their own anxiety. Mothers' RSA reactivity was measured between a resting baseline and a standardized laboratory task, and overprotective parenting was observed in that task. Toddler fearful temperament (FT) was observed in a separate standardized task as well as reported by mothers. At child age 3, mothers' overprotective parenting behaviors were observed according to the same procedures so change from age 2 could be measured. Results revealed that maternal anxiety and maternal RSA at age 2 interacted to predict relative increases in overprotective parenting behaviors at age 3. At low levels of RSA reactivity, reflecting RSA suppression, maternal anxiety predicted lower levels of overprotective parenting. At high levels of RSA reactivity, reflecting RSA augmentation, maternal anxiety predicted higher levels of overprotective parenting. Our results suggest that RSA suppression may protect mothers with anxiety symptoms from engaging in overprotective parenting, whereas RSA augmentation may put mothers with anxiety symptoms at risk for engaging in overprotective parenting. Findings indicate that the interaction of multiple parental traits should be considered when working with parents and families on parenting behavior. (PsycInfo Database Record (c) 2022 APA, all rights reserved).