Background <p>Numerous studies have been conducted regarding maternal bonding; however, there is a lack of studies investigating the association with unintended pregnancy. This study aimed to examine the effects of unintended pregnancy on maternal bonding using a longitudinal design from pregnancy to one month postpartum.</p> Methods <p>Participants were 78 mothers who attended the Department of Obstetrics for prenatal care at 20.5 weeks of gestational age. They responded to the Postpartum Bonding Questionnaire (PBQ) and the Edinburgh Postnatal Depression Scale (EPDS). Furthermore, we asked whether the pregnancy was unintended. At one month postpartum, they responded to the questionnaires again. We performed two-way repeated-measures analysis of variance to assess the effect of group (unintended pregnancy or intended pregnancy) and time (during pregnancy or one month postpartum) on the PBQ and EPDS scores.</p> Results <p>Mothers who had unintended pregnancies had significantly impaired maternal bonding compared to expected pregnancy mothers, both during pregnancy and one month postpartum. In addition, both unintended and expected pregnancy mothers had significantly decreased impaired maternal bonding at one month postpartum. Regarding depression, mothers with unintended pregnancy had significantly higher EPDS scores than mothers with expected pregnancy, both during pregnancy and one month postpartum.</p> Conclusions <p>Our findings emphasize that healthcare providers should promptly identify mothers with unintended pregnancies and conduct thorough assessments of mother-infant interactions postpartum.</p>