Objectives: Effective interventions such as non-nutritive sucking (NNS) improve neonatal development. The current study aimed at assessing the effect of NNS intervention by mothers on physiological factors, duration of full oral feeding attainment, and the length of hospital stay. Methods: The current clinical trial was conducted in the neonatal care unit (NICU) of Arash hospital affiliated to Tehran University of Medical Sciences, Tehran, Iran. The study was conducted on 2 groups of 38 preterm neonates. Neonates had gestational age of 26-34 weeks and received gavage feeding. They did not have assisted ventilation. Control neonates received routine care, whereas the intervention neonates received 3 NNS sessions done by mothers during the first 10 minutes of tube feeding per day. Data collection instrument included a mother-infant demographic form and an observation checklist of infant's physiological features. The date of full feeding and length of hospitalization were recorded. Results: Findings did not show any statistically significant correlation between groups in physiological features. Duration of full oral feeding attainment in the intervention and control groups were 22 ± 14.51 and 30.05 ± 18.58 days, respectively. The length of hospital stay in the intervention and control groups were 31.26 ± 16.89 and 41.82 ± 23.07 days, respectively. Then, non-nutritive sucking by mother's finger sped up the duration of full oral feeding attainment and reduced the hospitalization. Conclusions: Since NNS does not require skill and expertise, participation of mother is recommended. Then, infants benefit from not only the positive effects of NNS, but also mother-infant interaction.