Attachment security may be a mechanism by which exposure to early life adversity affects subsequent generations. We used a prospective cohort design to examine this possibility in a convenience sample of 124 women (age = 23–45 years, M = 32.32 [SD = 4.83] years; 57.3% White, 22.6% Asian) who provided self-reports of attachment style during pregnancy using the Attachment Style Questionnaire, of whom 96 (age = 28–50 years, M = 36.67 [SD = 4.90] years; 60.4% White, 19.8% Asian) were reassessed when their child was preschool-age (M = 4.38 [SD = 1.29] years). Women self-reported on their own childhood maltreatment severity and their child’s current emotional and behavioral problems using the Childhood Trauma Questionnaire and the Child Behavior Checklist for ages 1.5–5, respectively. Maternal childhood maltreatment severity was associated with less secure, and more avoidant and anxious attachment. Mediation analyses revealed further that less secure maternal attachment, but not avoidant or anxious attachment, mediated the associations between maternal childhood maltreatment and offspring emotional and behavioral problems. These findings suggest that improving maternal attachment security, which can be identified even prior to the child’s birth, is an important target to consider for intervention efforts aimed at minimizing adverse intergenerational effects of early life adversity.