Re-establishing breastfeeding (relactation) is necessary in preterm infants who are deprived of breastfeeding due to hospitalized in the neonatal intensive care unit (NICU). Although NICU nurses train mothers about breastfeeding and relactation to some degree, there exists a lack of support or evaluation for restarting breastfeeding. The present study tried to determine the effects of an educational and supportive relactation program on weight gain of preterm infants. This clinical trial study was performed on 60 preterm infants with mean gestational age of 29 weeks hospitalized in NICU of Alzahra Hospital (Tabriz, Iran). The infants were evaluated in two groups of 30. The mothers of infants in the control group received routine training and support about relactation while the intervention group received routine training as well as the designed educational and supportive relactation program including breast pumping, increasing milk agents and kangaroo mother care. Daily follow-up was conducted by the researcher. All the infants were weighed by a co-researcher. On the 14 th day of the study, the mean (SD) weight of infants in the control and intervention groups was 1666.67 (136.08) and 1765.86 (156.96) g, respectively. Providing mothers with support from the medical team and training on relactation and kangaroo mother care can lead to better weight gain of the low birth weight premature infants.