Breastfeeding is a health promoting social behavior but statistics suggest a persistent disparity of lower rates among African American mothers. The Theory of Normative Social Behavior (TNSB) explains when and how norms influence behaviors, but has produced inconsistent results with respect to proposed moderators group identity and injunctive norms (IN), limiting its predictive value in diverse cultural groups. Cultural norms are one of many influences on breastfeeding behaviors, yet little is known about their mechanisms of influence. The TNSB has not been tested in the breastfeeding context or within an exclusively African American cultural group. Given this knowledge gap, a survey of 528 African American mothers in the Washington, D.C. area was conducted to test the moderating effects of IN and subjective norms (SN) and social identity on the descriptive norms (DN) to intentions relationship as predicted by the TNSB. Structural equation modeling was used to show that when controlling for education and breastfeeding history, norms significantly predicted 26.4% of the variance in breastfeeding intentions. SN and DN interacted negatively to enhance breastfeeding intentions. Latent profile analysis using ethnic pride, collectivism, and religiosity scales detected four profiles of African American social identity. Social identity profile membership was a significant moderator on the DN to intentions pathway in the structural equation model. Profiles with the highest ethnic pride were significantly influenced by DN to intend to breastfeed. Implications from this study for public health intervention and communication messaging are discussed.