ABSTRACT Breast milk and breastfeeding bring considerable benefits to infants. A caveat in breastfeeding promotion efforts is the lack of emphasis on exclusive breastfeeding (EBF) for the first six months of a baby’s life. This research examined the relative effectiveness of descriptive and injunctive messaging on promoting 6-month EBF by employing a 3 (norms: descriptive norms vs. injunctive norms vs. no norms) X 2 (positive outcome recipient: baby vs. mother) factorial design and tested hypotheses with expecting women. Participants showed strong intention to exclusively breastfeed across experimental conditions. The results revealed that the descriptive normative message was more effective in promoting EBF than the control condition, whereas the injunctive normative message had no advantage over the control condition. Moreover, perceived outcome expectations for the baby and the mother attenuated the relationship between perceived descriptive norms and EBF intention. Theoretical and practical implications regarding how norms messaging can promote EBF are discussed.