RESUMEN
Breastfeeding self-efficacy is one of the indicators associated with the mental health of puerperal women and the maintenance of exclusive breastfeeding. OBJECTIVE: To evaluate the psychometric properties of an instrument to measure self-efficacy to breastfeed on the second postpartum day in the Chilean population. SUBJECTS AND METHOD: A convenience sample of 320 puerperal women who volunteered to participate in an interview on their second postpartum day was evaluated. Reliability was evaluated using the coefficient Cronbach's alpha. To assess its factorial structure, an exploratory factor analysis was performed. RESULTS: The results indicate that the final instrument, which has the factors "Intrapersonal Thoughts", composed of six items and "Breastfeeding Techniques", composed of eight items, presented an internal consistency by factor and total scale of F1 = 0.90, F2 = 0.91, and Total = 0.94, respectively. CONCLUSION: The breastfeeding self-efficacy scale showed good psychome tric characteristics during the second postpartum day among Chilean puerperal women.