Objective To investigate the expression of immunoglobulin (Ig) G4 and helper T cell (Th) 1/Th2 cytokines in the serum of patients with myeloperoxidase-anti-neutrophil cytoplasmic antibody-associated vasculitis (MPOAAV).Methods Serum samples of 50 AAV patients and 40 healthy controls who taking a physical examination in the same period were collected from The Second Affiliated Hospital of Soochow University. The levels of IgG and IgG4 were detected by immunoturbidimetry and enzyme-linked immunosorbent assay, respectively. The expression of Th1/Th2 cytokines in serum was detected by flow cytometry microsphere array (CBA). The differences of the above indexes between the 2 groups were observed, and the correlations between different indexes were analyzed.Results Serum samples were collected from all the 50 AAV patients, including 40 of MPO-AAV patients (80.0%). In the MPO-AAV group, the serum IgG4 level was (1.13±0.33) g/L, IgG4/IgG ratio was 0.094±0.032, IL-4 level was (2.54±0.68) pg/mL, and IL-6 level was 15.22 (8.83, 59.52) pg/mL, which were significantly higher than those in the control group (IgG4: ［ 0.80±0.27］ g/L, IgG4/IgG ratio: 0.070±0.028, IL-4: ［1.96±0.60］ pg/mL and IL-6: 4.95 ［2.82, 13.25］ pg/mL; all P＜0.01), and there was a positive correlation between the serum IgG4 and IL-6 levels in the MPO-AAV patients (r_s＝0.508, P＜0.05).Conclusion The proportion of MPO-AAV patients is high in AAV patients in our hospital. The serum IgG4, IL-4 and IL-6 levels in MPO-AAV patients are significantly increased, and the level of IgG4 is positively correlated with the level of IL-6, suggesting that the increase of IgG4 is related to the imbalance of Th1/Th2 cytokines in MPO-AAV patients.