Adolescent delinquency is a growing concern in different parts of the world and role of peer relations in delinquent behavior is well-researched subject. However, relationship between peer relations, self-concept, social identity, and delinquency is less known. This study examined the mediating effects of self-concept and social identity between peer relations and delinquency among adolescents in Pakistan. Survey research design was used through convenient sampling to collect data. The sample comprised of adolescents (N = 498; 218 female and 280 male adolescents) aged 11-18 years old. Participants provided data on questionnaires measuring self-concept, social identity, peer relations, and delinquency. Findings revealed that peer relation has significant impact on delinquency behavior and social identity of adolescents. However, peer relation was not found connected with self-concept significantly. Findings further indicated that social identity played meditating role between the relationship of peer relation and delinquency while self-concept did not mediate the impact of peer relation on delinquency. This study is helpful in determining factors leading to delinquency behavior and how delinquency behavior can be reduced by working on self-concept and social identity.