The aim of this study was to determine the effect of sleep quality of postpartum women on perception of insufficient milk and attitude to breastfeeding. The research was designed as a cross-sectional study. It was carried out with 347 mothers in a university hospital between December 2021 and July 2022. Data was collected via a personal informational form, the Postpartum Sleep Quality Scale (PSQS), the Perception of Insufficient Milk (PIM) Questionnaire and the Breastfeeding Attitude Rating Scale (BAAS). According to the results of the correlation analysis, there was a statistically significant negative relationship between the total mean score of the Postpartum Sleep Quality Scale and the mean total score of both the Perception of Insufficient Milk and the Breastfeeding Attitude Assessment Scale (r = -0.340, p = 0.000 and r = -0.153, p = 0.002 respectively). Examining the variables relating to the PIM score, a statistically significant correlation was found between age, PSQS, education level (bachelor's graduates and above), mode of birth (general anesthesia and cesarean) and breastfeeding experience (previously having given birth or having breastfed a baby) [(R = 0.448; R[superscript 2] = 0.200; F(5.341) = 17,096; p < 0.001)]. Mothers often need support to improve their sleep quality, as inadequate milk perception develops due to inadequate milk perception in the early postpartum period and changes their breastfeeding attitudes.