The potential indirect effect of observed maternal sensitivity at 5 months on the development of infants' behavioral regulation of emotion from 5 to 10 months (i.e., distraction and maternal-orientation behaviors) via infant's vagal withdrawal was investigated (N = 230). Results indicated that maternal sensitivity at 5 months was not directly associated with behavioral regulation at 10 months. However, greater maternal sensitivity at 5 months was associated with greater vagal withdrawal at 10 months, after controlling for vagal withdrawal at 5 months. Further, vagal withdrawal at 10 months was associated with greater orientation toward the mother at 10 months, after controlling for 5-month orientation behaviors. The indirect effect of maternal sensitivity on maternal-orientation behaviors was significant, suggesting that infant's vagal withdrawal may be one potential mechanism through which maternal sensitivity is related to behavioral regulation.