We aimed to investigate the neutrophil-lymphocyte ratio and platelet-lymphocyte ratio in adolescents with major depression. Sixty-seven adolescents and 121 healthy controls were enrolled in the study. The diagnosis was made by using both the Kiddie and Young Adult Schedule for Affective Disorders and Schizophrenia Present and Lifetime Version and the diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition. The severity of depressive symptoms was evaluated using the Beck depression inventory (BDI). The neutrophil-lymphocyte ratios of the adolescents with depression were significantly higher than those of the control group, even after adjusting for age, sex, BMI, and BDI scores, whereas there was no significant difference in platelet-lymphocyte ratios. A positive correlation between the severity of depression and neutrophil-lymphocyte ratios and platelet-lymphocyte ratios were determined in the case group. The results of this study may promote the hypothesis that inflammation plays an important role in the etiology of major depression in adolescents.