The objective of this study was to determine the effect of an education short course on professional¿ self-efficacy in the area of breastfeeding care. The intervention had a pre-post design. A total of 43 healthcare professionals attended the course. The Kirkpatrick model for the development, implementation and evaluation of education actions was used for a 4.5-h course. The aspects evaluated included professionals¿ satisfaction and learning regarding confidence to support lactating mothers, perceived transfer of knowledge to the workplace and organizational changes. Data were collected using self-administered questionnaires (participants, unit managers, and education planners), before and after the intervention. Participants' satisfaction with the education action was high in all of the aspects measured (greater than 3.9 in scores of 0¿5). Professionals showed a significant increase in self-efficacy levels for supporting breastfeeding (Wilcoxon test p-value = < 0.05, before intervention: median = 55, [IQR] = 11; after intervention: median = 60, [IQR] = 14). Participants, managers and organizers of the course identified changes in the way that professionals cared for breastfeeding mothers. In conclusion, this educational intervention enhanced professional self-efficacy and performance in breastfeeding care.