This study was designed to explore the association between CAG repeats in AR gene and major depressive disorder (MDD) in male children and adolescents. The results showed that there were differences between adolescent depressive patients and adolescent controls in CAG repeats' length and alleles' distributions, and the severity of depression and anxiety was negatively correlated with the length of CAG repeats in adolescent patients. This suggested that AR gene might be involved in the depressive upset in adolescents, and the age- and sex-related prevalent differences might also be associated to CAG repeats.