To evaluate breastfeeding in babies up to six months of age before and after frenotomy surgery in a reference hospital in a city from Santa Catarina state. Methods: An observational quality improvement study, carried out with babies up to six months of age undergoing frenotomy and their mothers in a reference hospital in southern Santa Catarina state. A questionnaire was applied to the mothers in two moments (before and after the surgery), with information regarding breastfeeding, sociodemographic, anthropometric and behavioral characteristics of them and of the babies. Descriptive analyzes were performed and the association between breastfeeding and the independent variables was assessed through Pearson’s chi-square and Fisher’s exact tests, using a 5% significance level. Results: A total of 74 children were studied, with 48 of them returning after surgery. 83.8% were breastfed before surgery and 64.9% after surgery. Before surgery, 58.1% of children effectively took the breast at once. After surgery, this prevalence was 83.3% (p=0.015). Before surgery, 75.9% of the mothers reported not feeling pain, while, after surgery, almost all of them (95.8%) reported this (p=0.004). Most mothers reported improvement in grip (83.3%), increase in the duration of breastfeeding (69.0%), improvement of baby’s breathing (75.0%), and an increase in the frequency of breastfeeding (51.7%). Conclusions: There was a decrease in the prevalence of breastfeeding after frenotomy. However, there was an improvement in the babies ‘grip and breathing and a reduction in the mothers’ pain when breastfeeding. It is emphasized the need to implement multidisciplinary actions in both primary and hospital care to assist mothers in order to prolong the duration of exclusive breastfeeding.