This is a descriptive study, with a qualitative approach, aimed to identify the knowledge of puerperal women on exclusive breastfeeding. Data were collected between September-October 2011, through semi-structured interview. Thirteen puerperal women, interned in a rooming unit of a public institution in the city of Caxias do Sul-RS, participated in the study. Data analysis was performed using thematic analysis. From the interpretation of information three categories emerged: the knowledge about exclusive breastfeeding, the breastfeeding process and the influences of received information. Even getting information from health professionals in the prenatal period, it is possible to understand that there is a need to improve communication and monitoring of mothers, as a continuity of professional care in the postpartum period, and also later, in the remote.