Background: Childhood obesity is a public health problem with significant long-term implications and racial/ethnic disparities. African American extended family members play a significant role in child rearing and socialization, and research suggests that grandparents, in general, may influence children’s weight-related behaviors. There is, however, a lack of research exploring how urban African American children’s relationships with extended family members may influence children’s weight-related behaviors. Therefore, this study examines how extended family members’ roles and responsibilities may influence urban African American children’s weight-related behaviors, how extended family members socialize children to adopt weight-related behaviors, and how extended family members’ socialization practices may differ from those of primary caregivers. Methods: This study builds upon and extends the work of a previous, mixed-methods study of 31 primary caregiver-child dyads, which was designed to examine household and neighborhood factors related to childhood obesity. In Phase 2, individual semi-structured, in-depth interviews were conducted with 8 Baltimore City children; paired interviews were conducted with their primary caregivers and one adult member of each child’s extended family. Manuscript 1 combines qualitative data from both studies to present case studies of the 4 families that participated in both studies. Manuscripts 2 and 3 focus on data collected from Phase 2’s 8 family units, and present detailed analyses of familial influences on children’s physical activity and dietary behaviors, respectively. Findings: Manuscript 1 indicates that mothers and extended family members may differ in their influences on children’s weight-related behaviors, which may be related to differences in the adults’ roles and responsibilities with the children. Manuscript 2 suggests that extended family members may be more physically active with children; this may be influenced by perceived familial closeness and different relationship dynamics. Manuscript 3 indicates that children are consistently taught to value food-based family traditions; however, adults may be inconsistent in the socialization strategies used in day-to-day dietary routines. These findings suggest that future family-based obesity interventions for African American children should extend beyond the immediate family to include key extended family members and consider the extended family networks’ norms and values.