Objective: The purpose of this study was to explore the mediating effects of parenting efficacy on the relationship between parenting alliance and parenting stress, and to investigate whether the relationships between these indicators were the same for mothers and fathers. Methods: A sample of 228 parents (114 mothers and 114 fathers) of 6 month old infants in Gyeonggi Province completed measures of Perceived Parenting Competence, Parenting Alliance Inventory, and Parenting Stress Inventory—Short Form. Results: The results indicated that parenting alliance produced its effect directly and indirectly through parenting efficacy on parenting stress. Using multiple group SEM analyses, it revealed that fathers parenting efficacy was mediated by parenting alliance and that the strength of the pathways was stronger for fathers than for mothers. Conclusion/Implications: These findings suggest that parenting alliance can improve father's parenting efficacy. The differential predictors of mother and father efficacy as well as their implications for future research are discussed.