Objective To evaluate the influence of grandmothers of infants on exclusive breastfeeding, from their perspective.Methods A descriptive cross-sectional study was carried out with 91 women from a hospital in the inland state of São Paulo. By means of a questionnaire, the following data were collected: sociodemographic data of the grandmother, mother and child; duration of exclusive breastfeeding of daughter or daughter-in-law; information on kinship of participant and grandchild; kind of help provided by grandmother; and knowledge about breastfeeding.Results The prevalence of infants on exclusive breastfeeding at two months was 35.17%; a total of 67.3% of grandmothers considered it important to give food to babies before six months of life, and 54% considered relevant breastfeeding at regular intervals. Moreover, 40% believed in weak milk and were not aware of signs of sufficient breast milk. Of the grandmothers interviewed, 69% had already offered tea and water to their grandchildren. In the univariate analysis, the maternal grandmother was more involved and close to the pair mother and child.Conclusion The presence of grandmothers influences in exclusive breastfeeding.