This study investigated the relationship between newborn feeding behaviour and feeding type among month-old babies and explored maternal and neonatal factors associated with breastfeeding rates at 1 month of age. This observational study was conducted in Japan with healthy mothers and full-term newborns. Newborn feeding behaviours were assessed using the Japanese Infant Breastfeeding Assessment Tool (IBFAT) within approximately 1 day of birth. Obstetric and newborn characteristics, including newborn feeding behaviours, were investigated in relation feeding type (breast milk or mixed milk) at 1 month of age. This study included 176 mother-newborn pairs. IBFAT scores were significantly higher in the breast-milk group (Median (M) = 10.5, Interquartile Ranges (IQR): 9.0-11.0) than in the mixed-milk group (M = 10.0, IQR: 7.5-11.0) (P = 0.046). Additionally, the sucking pattern of breastfeeding was showing a greater distribution of higher scores in the breast-milk group (M = 2.0, IQR: 2.0-2.5) than in the mixed-milk group (M = 2.0, IQR: 1.5-2.5) (P = 0.015). Compared to mothers who received epidural analgesia or synthetic oxytocin, primiparas who did not receive them were more likely to breastfeed (epidural analgesia: (33.3% vs. 65.8%, P = 0.004); synthetic oxytocin: (42.0% vs. 78.6%, P = 0.018)). For multiparas, Apgar and IBFAT scores were associated with feeding type at 1 month of age. This study found that newborns' effective and sustained sucking within 1 day of birth is an important factor for breastfeeding at 1 month of age. When assessing feeding type, maternal factors such as epidural analgesia should be the focus for primiparas, while neonatal factors such as feeding behaviour should be prioritised for multiparas.