Breastfeeding difficulties are often present in the first weeks of the postpartum period, and various factors can cause a mother's early cessation of breastfeeding. Such factors include mothers' self-efficacy and perception of insufficient milk. This study aimed to examine the effect of a hot application on the breast with the help of the Thera Pearl in the postpartum period on milk perception and breastfeeding self-efficacy. This was a randomized controlled trial. This study was completed with 64 puerperal mothers, 31 of whom were control and 33 were experimental. A Personal Information Form, Breastfeeding Observation Form, Breastfeeding Self-Efficacy Scale, and Insufficient Milk Perception Scale were used to collect data. The average breastfeeding self-efficacy scale scores of the experimental group were 42.46 and 62, respectively, at the first and last follow-up, while the control group's mean scores were 57.42 and 47. The average scores of the experimental group on the insufficient milk perception scale were 19, 28, and 48, respectively, from the first to the last follow-up, while those of the control group were 28, 24, and 34, respectively. As a result, self-efficacy and milk perception are important factors affecting breastfeeding. In this study, we found that Thera Pearl application increased breastfeeding self-efficacy but did not affect milk perception.