Introduction: Postpartum is one of the most important period in terms of physiological, psychological, and social changes. Feeling lonely during postpartum can affect women's interest in social support and baby. Aim: The study was conducted to determine the relationship between loneliness in postpartum women and social support, breastfeeding self-efficacy, and maternal attachment. Method: The descriptive-correlational research was conducted in a research hospital in Malatya. The data were collected within the first 24 hours of postpartum with 391 puerperal women who gave birth between July and October 2018. Data was gathered using Personal Information Survey, UCLA Loneliness Scale, Multidimensional Scale of Perceived Social Support, Breastfeeding Self-Efficacy Scale, and Maternal Attachment Scale. Results: The average age of the puerperal women was 27.91 ± 5.74, 27.9% were secondary school graduates, and 72.1% were multiparous. Postpartum women (93.9%) experienced moderate loneliness. The mean score of the postpartum women's UCLA Loneliness Scale was 49.77 ± 5.28, Multidimensional Perceived Social Support Scale score was 70.86 ± 14.26, Breastfeeding Self- Efficacy Scale score was 59.81 ± 10.14, and Maternal Attachment Scale score was 100.42 ± 7.09. Analyses showed a statistically significant low negative correlation between the UCLA Loneliness Scale and Multidimensional Scale of Perceived Social Support, and Breastfeeding Self-Efficacy Scale (r= -0.193, p=0.000; r= -0.132, p=0.009, respectively). There was no statistically significant relationship between UCLA Loneliness Scale and the Maternal Attachment Scale (p > 0.05). Conclusion: : Social support and breastfeeding self-efficacy decrease as loneliness increases in postpartum. Loneliness in postpartum women was not related to maternal attachment.