To assess how non-nutritive sucking (NNS) using a pacifier affected physiological and behavioral outcomes of preterm infants.Short-term longitudinal, experimental design.The study took place at the neonatal intensive care unit at Al-Mansoura, Egypt.Forty-seven preterm infants were divided into intervention and control groups. Preterm infants in the intervention group received NNS during nasogastric tube feeding while infants in the control group never received NNS. During 10 days, behavioral responses were videotaped and physiological responses were monitored.Significantly higher oxygen saturation occurred during and after nasogastric feeding for the intervention infants as compared to the control group. No significant group differences occurred in heart rate. The NNS group showed an accelerated transition to nipple feeding and had better weight gain and earlier discharge.Non-nutritive sucking was found to improve physiological and behavioral responses of preterm infants.