Most preterm infants exhibit atypical and immature feeding skills. Even though preterm infants have fulfilled the oral feeding readiness criteria, they still do not have optimal oral feeding ability. This study aimed to determine various factors affecting oral feeding ability in Indonesian preterm infants who have fulfilled oral feeding readiness criteria but still have not been able to feed orally. A cross-sectional study included 120 preterm infants admitted to five tertiary hospitals in Jakarta, Indonesia. Participants were preterm infants born at 28–34 weeks gestational age who had fulfilled the oral feeding readiness as the inclusion criteria: (1) stable cardiorespiratory status, (2) have achieved full enteral feeding via orogastric tube (OGT) 120 mL/kg/day without vomiting or bloating, and (3) strong and rhythmic non-nutritive sucking (NNS) through objective measurement. Infants’ oral feeding ability and various factors that were assumed to affect oral feeding ability, including physiological flexion postural tone, physiological stability, rooting reflex, self-regulation, behavioral state, and level of morbidity were evaluated. Chi-square and multivariate analysis with Poisson regression were performed. Results indicated that postural tone, rooting reflex, physiological stability, self-regulation, behavioral state, and level of morbidity were significantly related to oral feeding ability in preterm infants. The most influencing factors were self-regulation with a prevalence ratio (PR) of 1.96 (1.16–3.34; CI 95%) and p = 0.012, followed by postural tone, high morbidity, and behavioral state (PR 1.91; 1.59; 1.56; CI 95%, respectively). In conclusion, despite meeting the oral feeding readiness criteria, most preterm infants were still not able to feed orally. There are other factors affecting oral feeding ability in Indonesian preterm infants.