Objective To analyze the clinical characteristics of vasculitis associated with antineutrophil cytoplasmic antibody against myeloperoxidase (MPO-ANCA),and to investigate preliminarily the relationship between MPO-ANCA and the clinical damages.Methods One hundred and thirty-two patients with primary antineutrophil cytoplasmic antibody (ANCA) associated vasculitis,which were diagnosed for the first time,were involved into this prospective study.All the patients had positive laboratory tests for peri-nuclear ANCA (p-ANCA) and MPO-ANCA.The characteristics of their clinical presentations were analyzed.The levels of p-ANCA and MPO-ANCA in the peripheral blood were detected and the relationship between the levels and the damages were explored.T-test and Spearman rank correlation analysis were used for statistical analysis.Results Of the 132 patients from 8 different clinical departments,128 (97.0％) were microscopic polyangiitis (MPA),3 (2.3％) were granulomatosis with polyangiitis (GPA),and 1 (0.7％) was eosinophilic granulomatosis with polyangiitis (EGPA).The mean age was (62±15) years old.The average time between onset of the disease and diagnosis was (10 ±18) months,and only 14 (10.6％) were diagnosed within one month.Among the major organ involvements,the occurrence of renal,lung,joint,heart,peripheral nerve,skin,and central nerve involvement was 72.0％(95 cases),67.4％(89 cases),26.5％(35 cases),19.7％ (26 cases),17.4％(23 cases),10.6％(14 cases) and 9.8％(13 cases),respectively.Lung was more susceptible to be involved among the aged in their early course [(66±11) years,(55±19) years,t=-3.478,P＜0.01; (6±10) months,(18±27) months,t=2.920,P＜0.01],and joint involvement was more common in the younger [(57±18) years vs (64±13) years,t=2.335,P＜0.05] patients.p-ANCA had no relationship with the disease activity or the range of organ involvements(r=0.013,P＞0.05; r=0.087,P＞0.05).MPO-ANCA had a positive association with disease activity but had no significant correlation with the range of organ involvements(r=0.258,P＜0.01; r=0.022,P＞0.05).Conclusion The MPO-ANCA associated vasculitis is not rare in our country.MPA is the most common vasculitis which mainly affects the aged population,and its diagnosis is often delayed due to the lack of characteristic clinical presentations.It is possible that MPO-ANCA may play a pathogenic role in vasculitis,and the various clinical manifestations might be related with the specificities of MPO-ANCA.