The aim of this study was to determine the effect of kangaroo mother care, provided in the early postpartum period, on the breastfeeding self-efficacy level and the perceived insufficient milk supply. This study was conducted as the quasi-experimental design. The population of the study consisted of the mothers and their infants, to whom they gave birth in a university hospitals located in either eastern or western Turkey, between December 2016 and June 2017. In this study, mothers and their infants were randomly assigned to the experimental group (kangaroo mother care, n = 30) and the control group (n = 30). This study included 2500 to 4000 g birth weight infants who had no serious health problems and no sucking problems. The Introductory Information Form, the Breastfeeding Self-Efficacy Scale, and the Perception of Insufficient Milk Questionnaire were used to collect the data. In this study, kangaroo mother care was provided as a nursing intervention for the mothers in the experimental group twice a day until they were discharged. Any other application was not performed in the control group's mothers apart from the routine application. Ethical principles were adhered in all stages of the study. The breastfeeding self-efficacy mean score (65.50 +/- 3.95) of the mothers who performed kangaroo mother care was higher than the mean score of the mothers who did not perform kangaroo mother care (55.50 +/- 7.00) (P < .001). In addition, mothers in the experimental group (46.60 +/- 3.40) perceived their milk more sufficiently than mothers in the control group (30.17 +/- 11.37) (P < .001). In the study, a statistically significant correlation was determined between breastfeeding self-efficacy levels of mothers in the experimental group and the perceived insufficient milk supply (P < .05). In the study, kangaroo mother care increased breastfeeding self-efficacy perception of the mothers and reduced the perceived insufficient milk supply. This shows that kangaroo mother care can potentially have an important effect on breastfeeding perceptions.