Objective <p>This study aims to explore the current situation and relationship between social support, body image, and breastfeeding self-efficacy in women during the third trimester of pregnancy. It also examines the mediating role of body image and provides evidence to promote prenatal breastfeeding self-efficacy.</p> Methods <p>A convenience sampling method was used to select 312 women in the third trimester of pregnancy who underwent prenatal examination at the obstetrics clinic of a tertiary hospital in a city from January to July 2023. A questionnaire was distributed to gather data.</p> Results <p>Body image was negatively correlated with both social support and breastfeeding self-efficacy (both <i>p</i> &lt; 0.05). Social support was positively correlated with breastfeeding self-efficacy (<i>p</i> &lt; 0.05). Factors influencing breastfeeding self-efficacy in the third trimester included per capita monthly income, method of medical expense payment, body image, and social support, which together explained 53.5% of the total variance. Additionally, body image partially mediated the relationship between social support and breastfeeding self-efficacy.</p> Conclusion <p>In addition to enhancing social support for pregnant women, healthcare professionals can improve women’s body image in the third trimester by focusing more on this aspect, which can, in turn, enhance breastfeeding self-efficacy prior to childbirth.</p>