Objective To investigate the change of circulating follicular helper T cells (cTfh) in patients with anti-neutrophil cytoplasmic myeloperoxidase antibody-associated vasculitis (MPO-AAV), and to analyze the relationship between cTfh and disease activity. Methods Thirty-eight untreated MPO-AAV patients (patient group) and thirty-eight healthy volunteers (control group) were enrolled in this study. cTfh and membrane expression of inducible co-stimulator(ICOS)and programmed cell death protein 1(PD-1) were detected by flow cytometry (FCM). Serum anti-neutrophil cytoplasmic myeloperoxidase antibody (MPO-ANCA) was measured by ELISA. Disease activity was evaluated by Birmingham vasculitis activity score (BVAS). Results Compared with those in control group, the proportions of cTfh, ICOS+Tfh and PD-1+Tfh cells in patient group were significantly higher [(25.9±3.8)％vs. (21.0±5.3)％, P<0.001;(1.8±0.8)％vs. (0.8±0.5)％, P<0.001 and (10.2±2.8)％vs. (8.2±2.2)％, P=0.001, respectively]. Meanwhile, the expression of ICOS and PD-1 on cTfh in patient group was markedly more intensive (59.6±10.0 vs.49.2±6.9, P<0.001 and 532.6±104.2 vs. 485.1±73.4, P=0.025, respectively). In patient group, the proportion of cTfh was positively correlated with the ratio of ICOS+Tfh, the expression of ICOS, the level of MPO-ANCA and BVAS (r=0.407, P=0.011; r=0.705, P<0.001; r=0.737, P<0.001 and r=0.663, P<0.001, respectively). The expression intensity of ICOS on cTfh was positively associated with ICOS+Tfh ratio, serum MPO-ANCA and BVAS (r=0.388, P=0.016; r=0.645, P<0.001 and r=0.653, P<0.001, respectively). Nevertheless, the expression of PD-1 on cTfh was only positively correlated with the ratio of PD-1+Tfh (r=0.473, P=0.003). Conclusions Enhanced cTfh in patients with MPO-AAV might produce MPO-ANCA, which is related to the aggravation of MPO-AAV. Thus, cTfh and its ICOS could be potentially targeted for the treatment of MPO-AAV.