Background <p>This study aimed to systematically describe the characteristics of bonding disorders and diagnostically classify them using the Japanese version of the 6th Stafford Interview. We investigated the cut-off points of the Japanese version of the Mother-Infant Bonding Scale (MIBS-J) and Postpartum Bonding Questionnaire (PBQ) to screen for bonding disorders.</p> Methods <p>We recruited participants in their second trimester and studied 40 mother-infant dyads. At one month postpartum, we conducted the mother-infant relationship section of the Stafford Interview and classified participants into diagnostic groups. We administered the MIBS-J at four days and one month postpartum and the PBQ at one month, combined with the interview. We used the total scores to analyse the receiver operating characteristic curve at four days and one month.</p> Results <p>We diagnosed one case of emotional rejection and eleven cases of mild disorder. Additionally, three cases exhibited pathological anger with mild disorder—one with emotional rejection and one infant-focused anxiety case with normal bonding. The screening scores for bonding disorders, including mild cases, were 2 or more points for MIBS-J at four days and 3 or more points at one month. The PBQ was better at identifying severe bonding disorders, with a score of 19 or more points.</p> Conclusions <p>Bonding disorders can expose mothers to serious mental and parenting conditions as early as one month postpartum. Questionnaire screening and diagnostic interviews can help with early detection and care.</p>