The aim of this study was to investigate the effects of breastfeeding self-efficacy (BSE) and breastfeeding success (BFS) on infants' weight gain rates and breastfeeding outcomes. Mothers were evaluated within the postpartum 72 hours with "Breastfeeding Self-Efficacy Scale-Short Form (BSES-SF)" and "LATCH Scale." After 6 months, the mothers were called to learn the exclusive breastfeeding (EB) duration and the weight of the infants. Two hundred mother-infant couples were enrolled, 176 (88%) of them could be reached in the sixth month. The BSES-SF scores were positively correlated with LATCH scores (P = .0001). The EB rate in the sixth month was positively correlated with BFS but not correlated with BSE (r, P = .218, .004; .79, .297, respectively). The percentage of weight gain and the rate of weight percentile change of babies according to birth weight at the sixth month of age were negatively correlated with BSE (r = -0.226, -0.148, P = .003, .049, respectively) but not correlated with BFS. Higher BFS was associated with increased duration of EB in the first 6 months of life, and higher BSE was related to lower increase in the percentage of weight gain and a lower rate of weight percentile change of babies at 6 months of age.