The relationships between postpartum depression and demographic characteristics, social support, marital relationship, negative and passive acceptance of the mother role, and parenting behavior were examined in 215 mothers who live in Tokyo, Japan, and who have a child less than 1 year old. Social support from husbands or friends and marital relationship were found to be significantly related to the Edinburgh Postnatal Depression Scale (EPDS) score. Although negative and passive acceptance of the mother role was also related to the EPDS score and neglectful parenting behavior, it was not found to be related to aggressive parenting behavior. The correlation between EPDS score and neglectful or aggressive parenting behavior was also significant, with aggressive parenting behavior more strongly related to the EPDS score.