Objective The study aimed to determine the effect of breastfeeding support through social media on women's breastfeeding self-efficacy. Methods A randomised controlled trial was conducted in the maternity unit of Aksaray University Education and Research Hospital, Turkey. Education and counselling on breastfeeding were given via WhatsApp to women in the intervention group. Women in the control group received routine breastfeeding teaching before discharge from hospital. The Breastfeeding Self-Efficacy Scale-Short Form (BSES-SF) was administered to both groups immediately after birth and at 3 and 6 months postpartum. The study was completed by 31 women in the intervention group and 37 women in the control group. Results At 3 and 6 months there was a statistically significant difference in BSES-SF mean scores between the intervention and control groups (p < 0.05). BSES-SF scores in the intervention group were higher at 3 and 6 months compared with baseline, while BSES-SF scores in the control group were lower at 6 months compared with baseline. Conclusion Women's breastfeeding self-efficacy was improved through a social media-based teaching and counselling intervention. Health care professionals should make use of social media tools to improve women's breastfeeding self-efficacy and encourage continuity of breastfeeding.