This study aimed to identify the reasons which made mothers wean their children early and analyze their knowledge on breastfeeding. It is about a research of qualitative approach and was developed in Teresina-Pi, with 11(eleven) mothers, aged between 18 and 43 years old, who weaned early. The reports of the subjects, from the semi-structured interview, enabled the emergence of two categories: Understanding on breastfeeding and Factors that led to early weaning. The analyses showed that the factors which led to early weaning were: mother's illness that damaged the breastfeeding; medicines used by them and the feeding of the infants with another kind of food. It also put in evidence that the knowledge on breastfeeding is based on a strongly biomedical health-disease speech.