Purpose <p>The aim of this study is to determine the effect of supplemental nursing system on, sucking success, weight gain findings and bilirubin levels in newborns.</p> Design and methods <p>The study was conducted as a randomized controlled trial. The population of the research consisted of 71 infants who received care and treatment at the Neonatal Intensive Care Clinic of the hospital located in a province in eastern Turkey between February and June 2023. In the study, the “Infant Follow-up Form” to access the birth-related characteristics of infants and mothers, the “LATCH Breastfeeding Diagnostic Scale,” to diagnose the process of switching to full breastfeeding and the “Mother-Infant Communication Form” were used. The body weights of the infants were monitored using a Charder baby scale and bilirubin levels were measured using a Drager brand transcutaneous bilirubin measuring device.</p> Results <p>The difference between the groups in terms of the mean sucking success, weight gain findings and bilirubin levels scores was statistically significant (<i>p</i> &lt; 0.05).</p> Conclusions <p>Feeding an infant with the supplemental nursing system had a positive effect on sucking success, weight gain findings and bilirubin levels.</p>