OBJECTIVES: This pilot study aimed to 1) follow the longitudinal changes in the salivary oxytocin level of pregnant women from late pregnancy to early postpartum, 2) examine the factors related to these changes, and 3) clarify the association of these changes with mother-infant bonding. METHODS: This study used a longitudinal observational design and questionnaires to obtain objective and subjective data. For oxytocin evaluation, saliva samples were collected and their oxytocin levels were measured at 4-time points [i.e., 1) 36-37 gestation weeks, 2) 38-39 gestation weeks, 3) 1-2 days postpartum, 4) 4-5 days postpartum]. The oxytocin level was assayed in duplicates by enzyme-linked immunosorbent assay. Baseline data were evaluated using the Parental Bonding Instrument (25 items), State Trait Anxiety Inventory (20 items), and Center for Epidemiologic Studies Depression Scale. Postpartum data were evaluated using the Mother to Infant Bonding Scale Japanese Version (10 items), Maternity Blues Scale (13 items), and 'Fatigue after Childbirth' using the Visual Analogue Scale (VAS: 0-100 mm). RESULTS: The participants were 13 primiparas with a mean age of 33 years. They had no depression or anxiety at the baseline. Their mean salivary oxytocin levels significantly increased from late pregnancy (36-39 gestation weeks) up to 1 day postpartum and then decreased until 5 days postpartum. There was a negligible correlation between the bonding disorder and the salivary oxytocin level on the 5th day after childbirth. A moderate correlation was observed between the maternity blues score and the salivary oxytocin level. There was a significant negative correlation between the postpartum fatigue and the salivary oxytocin level 1 day and 5 days after childbirth. CONCLUSION: The mean salivary oxytocin levels significantly increased from the baseline up to 1 day postpartum and then decreased until 5 days postpartum. The salivary oxytocin level was moderately associated with maternity blues and significantly with postpartum fatigue.