Abstract: Objective To study the changes of brain activity in adolescent and adult patients with major depressive disorder(MDD), and to explore the commonness and difference of pathophysiological basis and pathogenesis between them for providing basis for accurate diagnosis and specific treatment of adolescent depression. Methods The volunteers were collected by means of advertisement recruitment, outpatient recommendation, and so on. After the demographic data collection and the evaluation and diagnosis of the scale, 30 first untreated adolescent depressive patients and 28 healthy controls, as well as 31 first untreated adult depressive patients and 34 healthy controls, were scanned for head resting state functional magnetic resonance(fMRI), and two samples of t test(GRF correction, P<0.05) were performed on 2 groups of adolescents and 2 adult groups of standard ALFF brain maps, respectively. The brain regions with significant difference were compared. Results Compared with the adolescent health control, the ALFF of Frontal_Sup_R(aal), Frontal_Sup_Medial_R(aal), Frontal_Mid_R(aal), Frontal_Sup_Orb_R(aal) were significantly increased in the adolescent depressive patients, no regions decreased. Compared with the adult health control, the ALFF of Insula(aal), Frontal_Inf_Oper(aal), Rolandic_Oper_R(aal),Precentral_R(aal), Putamen(aal) were significantly increased in adult depressive patients, no regions decreased. Conclusion Both Adolescents depression and adult depression have their own specific brain dysfunction, which showed increased activity, but no decreased activity. However, there still have some difference between them, suggesting that the neurobiological basis and pathogenesis of adolescent depression may be different from adult depression.