Background: Inventory of Parent and Peer Attachment (IPPA) has been widely used in various countries, in examining the effect of parent attachment on later mental health. However, a limited number of studies have verified its psychometric property, in particular, its three-factor structure originally proposed by Armsden & Greenberg. Purposes: This study aimed at examining whether or not the three-factor structure (Trust, Communication, Alienation) of the Japanese version of parent IPPA is valid and examining whether respondents' gender and/or their parents' gender affects their attachment security level. We further studied the hypothesis that parent attachment assessed by IPPA is influenced by past parenting, and will influence later mental health. Methods: Data from the questionnaire survey targeting Japanese college students was used for analyses. The three inventories: IPPA, Authoritarian parenting subscale from Parental Authority Questionnaire (PAQ), and Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM), were used in the analyses of this study. After confirming factor structures of father and mother IPPAs by confirmatory factor analyses (CFA), ANOVAs were conducted to see whether respondent and/or parent gender had effects on the attachment security level. Structural equation modelling (SEM) was conducted to demonstrate the pathways from past parenting to later mental health via parent attachment for men and women respectively. Results: Three-factor structures for both father and mother IPPAs were confirmed by removing one item from the Communication subscale. ANOVAs showed that, concerning Trust, there were no differences between male and female How to cite this paper: Uji, M., & Kawaguchi, M. ( 2024).