Puberty has been associated with increased parent-child conflict and disagreements. However, most research has considered adolescents in the midst or end of pubertal development, leaving potential links between early pubertal development and parent-child relationships relatively understudied. Moreover, studies have most often examined biologically related families where separation of underlying genetic and environmental effects on the associations between puberty and parent-child relationships is impossible. The current study addresses these gaps by investigating the aforementioned association in a sample of 11-year-old adolescents and their adoptive parents (N = 259 families). Results from cross-sectional analyses revealed significant associations between early pubertal maturation and paternal hostility, such that adolescents with early onset of puberty tended to experience increased levels of hostility with their adoptive fathers. With the utility of a genetically sensitive adoption-at-birth design, current findings demonstrate that the association between early pubertal maturation and family relationships in early adolescence could be partially explained by environmental factors.