The purpose of this study was to verify the mediating effect of parenting efficacy on parenting stress perceived by 3 month old infant’s mother. The subjects were 802 mothers of 3 month old infants living in Seoul and Gyeonggi-do. Data analysis was conducted using SPSS 23 and AMOS 23 to examine the correlation between parenting alliance, parenting efficacy and parenting stress perceived by mother with 3-month-old infant children.The results of this study were as follows: First, there was a significant correlation between parenting alliance, parenting efficacy, and parenting stress perceived by 3- month-old infant mothers. Second, the relationship between parenting alliance and parenting stress perceived by 3-month-old infant mother showed full mediation effect of parenting efficacy. The results of this study suggest that parenting efficacy can mediate parenting stress in relation to parenting alliance and parenting stress perceived by 3-month-old infant mothers. Based on the results of this study, we suggested ways to improve the mother's parenting efficacy and reduce parenting stress.