Objective To explore the significance of peptidylarginine deiminase type 4 (PAD4) in the pathogenesis of ANCA-associated vasculitis (AAV) by detecting its level in patients with AAV.Methods Sera from 13 patients with AAV,11 patients with primary chronic kidney disease and 12 healthy controls were collected.Serum PAD4 was detected using commercial ELISA kits.The association between serum PAD4 and BVAS of AAV was further investigated.Results (1) The serum level of PAD4 in patients with AAV in active and remission stages were all higher than that in the healthy controls.The serum level of PAD4 in patients with CKD was not found elevated compared with the normal controls.(2) The serum levels of PAD4 in AAV with renal damage were all significantly higher than that in CKD group no matter in active or remission stage.(3) The serum level of PAD4 in AAV with renal damage in active stage was positively correlated with BVAS (r=0.71,P=0.02).Conclusion PAD4 is involved in the pathogenesis of AAV.