This study focused on programs to promote breastfeeding in order to prevent early weaning of working mothers' infant children. A non-randomized intervention study was conducted using a survey of mothers who had returned to work after childbirth, including both participants and non-participants in a program to promote breastfeeding. The sample consisted of 200 mothers of infants ranging from 6 to 10 months of age. Factors associated with early weaning were analyzed with the chi-square and Fisher's exact tests and multiple logistic regression (α = 0.05). The results showed statistical differences between the groups in relation to exclusive breastfeeding (p < 0.0001) and breastfeeding (p < 0.0001). There was a statistically significant difference (p = 0.0056) between the groups in relation to time between childbirth and return to work. There was no difference between the end of maternity leave and weaning time. Mothers that were unable to nurse their infants during the work shift showed 4.98 times higher odds (95%CI: 1.27-19.61) of weaning them before the fourth month of age.