The aim of the study is to identify and compare the effect of pain, stress, and cortisol level during labor on breastfeeding success. The study was conducted with 51 pregnant women in the delivery room of Nenehatun Maternity Hospital between 15 August and 30 December 2016. The data were collected using the personal information form, visual analog scale (VAS), verbal category scale (VCS), perceived stress scale (PSS) and Breastfeeding Diagnostic and Assessment Scale (LATCH). It was determined that the total mean score of the mothers for the LATCH breastfeeding success scale was 6.56 ± 1.64, the perceived stress scale total mean score was 48.13 ± 4.09 in their active phase, and the perceived stress scale total mean score was 41.41 ± 5.78 in their postpartum period. A negative moderate significant correlation was observed between the LATCH breastfeeding success scale mean scores and the cortisol levels in the active phase and postpartum period. It was found that the LATCH had a significant correlation with the perceived stress and cortisol in the postpartum period. It was determined that the mothers had more stress in the active phase and this stress affected negatively the lactation and sucking behavior of the infant.