Anti-glomerular basement membrane (anti-GBM) disease and anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis both could cause rapidly progressive glomerulonephritis. The coexistence of ANCAs and anti-GBM antibodies was known as double positive, which was extremely rare in children. We report a pediatric case with coexistence of ANCAs and anti-GBM antibodies.A 6-year-old girl presented with acute renal failure, hematuria, proteinuria, and oliguria. She was double positive of ANCAs specific to myeloperoxidase, and anti-GBM antibodies. Kidney biopsy confirmed linear immunoglobulin (Ig)G deposit along GBM and 100% of crescent formation in glomeruli; among them 83.3% were cellular crescents. Human leukocyte antigen (HLA) gene typing showed DRB11501, an allele strongly associated with anti-GBM disease, and DRB10405, an independent risk factor for renal failure in patients with ANCA-associated vasculitis. The titer of anti-GBM antibodies was 1:800, and the predominant IgG subclass was IgG1, which was closely related with severe kidney injury and worse outcome. The target antigen of anti-GBM antibodies was restricted on the noncollagen domain 1 of the 3 chain of type IV collagen (3[IV]NC1), with recognitions to both epitopes, E-A (3(17-31)) and E-B (3(127-141)).This is the first reported pediatric case with coexistence of ANCAs and anti-GBM antibodies, in which the HLA typing and immunologic characters of autoantibodies were identified. The findings on this early-onset patient are meaningful for understanding the mechanisms of both anti-GBM disease and ANCA-associated vasculitis.