Background: Antineutrophil cytoplasmic antibody (ANCA)-associated systemic vasculitis (AASV) is a systemic autoimmune disease. A number of cases have been found to have antiglomerular basement membrane (GBM) antibody-positive serum. The purpose of the current article is to investigate the prevalence of anti-GBM antibodies in sera from a large cohort of Chinese patients with AASV and to characterize the clinical and pathological features of the ‘double positive’ patients. Methods: Sera from 652 patients with AASV were screened by enzyme-linked immunosorbent assay (ELISA) and confirmed by Western blot analysis using purified human α(IV)NC1 as antigen. Antigen specificity of anti-GBM antibodies was determined by ELISA using recombinant human α3(IV)NC1 as solid phase ligand. Clinical and pathological data of patients with both ANCA and anti-GBM antibodies were analyzed retrospectively. Results: 61/652 (9.36%) sera from patients with AASV were serum anti-GBM antibody positive and all recognized recombinant human α3(IV)NC1. All the cases had renal involvement, 37/48 (77.1%) cases had pulmonary involvement, non-specific symptoms and other multisystem involvements were common. The renal survival was 14.6% (7/48) and patient survival was 37.5% (18/48) respectively at the end of 1 year. The following factors predicted poor prognosis: (1) serum creatinine >700 µmol/l (p = 0.034); (2) oliguria or anuria on diagnosis (p = 0.001); (3) high percentage (>85%) of glomeruli with crescents (p = 0.011); (4) high titer anti-GBM antibodies (p = 0.003), and (5) hemoptysis (p = 0.049). Conclusion: Patients with double antibodies were not rare in AASV. They had multisystem involvement but poor short-term prognosis.Anti-GBM antibodies should be detected on diagnosis of AASV, especially for old ages.