Objective To investgate prevalence and clinical significance of antiproteinase 3(PR3)an- tibodies in Wegener's granulomatosis(WG)and other vasculitis patients.Methods One hundred and eleven systemic vasculitis patients with WG(9 cases,including 21 serums of tracking WG patients)and other systemic vasculitis(102 cases),403 secondnary vasculitis CTD(SLE 213 cases,RA 135 cases),nephritis 62 cases,30 healthy subjects were examined for anti-PR3 and anti-MPO antibody by enzyme-linked immunosorbent assay (ELISA)and ANCA by indirect immunofluorescence(IIF)was performed.Result Anti-PR3 positive were 23 in 588 serums of patients.The prevalence of anti-PR3 positive was WG(16/21,71.4 %),other systemic vas- culitis were not found anti-PR3,SLE(6/213,2.8%),RA(1/135,0.7%).In particular,the prevalence of anti- PR3 and cANCA with WG tended to be higher in the patients with other systemic and secondnary vasculitis (P＜0.05).The sensitivity and specificity of anti-PR3 for diagnosis of WG were 71.42% and 98.58%.The sensi- tivity and specificity of combination anti-PR3 and cANCA were 61.90% and 99.82%.Anti-PR3 and cANCA are associated with treament of WG.Conclusion Anti-PR3 antibody has high specificity for diagnosis of RA. Detection of anti-PR3 and cANCA at the same time can improve the specificity considerably.As sensitive markers of WG,anti-PR3 antibody may be useful for diagonosis and early treament.Anti-PR3 also may be useful for activity and relapse of WG.