Aim: This study investigated the effect of supplemental feeding tube device (SFTD) method on time to transition to exclusive breastfeeding and discharge time in preterm infants. Methods: This randomized controlled trial was conducted in the neonatal intensive care unit of a public hospital in Turkey (Clinical Trial Number: NCT05815706). The sample consisted of 65 preterm infants randomized into a control (n = 32) and an experimental (n = 33) group. The experimental group participants were SFTD-fed until they switched to exclusive breastfeeding. The control group participants were fed according to the routine procedure. Data were collected using a questionnaire, a Preterm Infant Monitoring Form, and the LATCH Breastfeeding Assessment Tool. The data were analyzed using numbers, percentage distributions, means, standard deviations, Pearson's chi-square test, and independent samples t-test. The study was approved by an Ethics Committee. Permission was obtained from the hospital. Informed consent was obtained from all parents. Results: The experimental group (123.64 ± 63.25 hours) demonstrated an earlier transition to exclusive breastfeeding compared with the control group (187.50 ± 95.30 hours) (p < 0.05). The experimental group (361.45 ± 110.46 hours) had significantly shorter hospital stays than the control group (479.25 ± 163.17 hours). The experimental group (35.33 ± 1.14 weeks) had a significantly younger gestational age at discharge than the control group (35.97 ± 1.03 weeks). Conclusion: The SFTD is an alternate supportive feeding method that helps preterm infants switch to exclusive breastfeeding sooner, have shorter hospital stays, and have a younger gestational age at discharge than their bottle-fed counterparts.