To understand the conditions that give rise to parenting self-efficacy in Japan and the United States, the authors have investigated its relation to the perceptions of support available to mothers of children in the final year of preschool (N = 235; n = 121 in United States, n = 114 in Japan). Hierarchical regression analysis indicates that in both countries, women who experience higher parenting self-efficacy report more positive childhood memories of parental support and greater satisfaction with husband’s and friends’ support. Mothers in the United States are significantly more self-efficacious than are mothers in Japan, even after controlling for the effects of the support predictors. A follow-up mediational analysis reveals that Japanese women’s lower levels of parenting self-efficacy are partially attributable to their low satisfaction with husband’s support.