Parenting style plays an important role in children's externalizing behaviors. Differences in physiological regulation among children may lead to variations in whether or to what extent parenting style influences them. The present study aimed to investigate the effect of parenting styles on young children's development of externalizing behaviors and to consider the moderating role of children's physiological regulation (resting respiratory sinus arrhythmia [resting RSA]). Participants included 119 Chinese parent-child dyads (55 girls, T1 M[subscript age] = 4.62 years, SD[subscript age] = 0.27 years; T2 M[subscript age] = 5.73 years, SD[subscript age] = 0.29 years). At T1, parents reported their parenting styles and children's externalizing behaviors; at T2, children's externalizing behaviors were measured again by parental reports, and children's resting RSA was measured. Authoritarian parenting predicted children's development of externalizing behaviors from T1 to T2, and this effect was moderated by children's resting RSA. For children with low resting RSA, authoritarian parenting positively predicted their development of externalizing behaviors, but no significant relation was found among children with high resting RSA. Permissive parenting was associated with children's externalizing behaviors T1 but not with the development of externalizing behaviors from T1 to T2. The present study demonstrates the crucial role of resting RSA in early childhood and supports the diathesis-stress model by revealing that children with poor physiological regulation are vulnerable to authoritarian parenting and thus develop high externalizing behaviors.