Enhancing the quality of services provided by child and adolescent social workers is crucial for promoting the healthy development of children and adolescents. However, limited research has integrated both organisational and individual factors into the examination of the influencing factors of social work service quality. This study uses the hierarchical linear model to study how organisational leadership can improve the service quality of child and adolescent social workers through the mediating influence of professional identity. The hypotheses were examined using data from 2,248 child and adolescent social workers in 157 social service organisations collected during the China Social Work Longitudinal Study in 2019. The findings reveal two critical insights: (i) there is a significant correlation between organisational leadership in social service organisations and the service quality provided by child and adolescent social workers and (ii) professional identity appears to play a fully mediating role in this relationship. These findings encourage the boards of social service organisations to implement appropriate measures for reinforcing internal governance, exporting effective leadership and nurturing the professional identity of child and adolescent social workers, thereby elevating the quality of their services.