Objectives To investigate the renal manifestations of patients with anti-neutrophil cytoplasmic antibodies (ANCA) associated vasculitis and impact of early diagnosis and treatment on renal function recovery.Methods The clinical and pathological data of 21 cases of ANCA associated small vessel vasculitis who were admitted in our hospital from January 2000 to August 2009 were analyzed, in which 18 of them underwent renal biopsy.Results 21 cases of ANCA associated vessel vasculitis was composed of 16 microscopic polyangiitis (MPA) ,3 Wegeners granulomatosis (WG) and 2 allergic granulomatous vasculitis (CSS) patients , with a mean age of 52. 5 ±11.5 years. The clinical extra-renal manifestations included fever,lower respiratory tract symptoms, lung imaging abnormalities , anemia and eye or nose involvement. Renal manifestation contained hematuria in 21 cases (100% ) , proteinuria in 19 cases (90.1% ) , normal serum creatinine level in 6 cases (28.5% ) and abnormal in 15 cases (71.4% ) ,8 cases(38.1% ) underwent dialysis. The pANCA and MPO-ANCA were positive in 16 cases, cANCA and PR3-ANCA positive in 3 cases, both pANCA / MPO-ANCA and cANCA/PR3-ANCA were positive in 1 case, and none was positive in 1 case. Renal biopsy showed segmental fibrinoid necrosis of small blood vessels and crescentic formation . No or trace immunoglobulin deposition were detected by immune fluorescence essay. Combination of corticosteroids with cyclophosphamide were administrated for all cases and plasma exchange added for severe cases. The renal function of 5 out of 7 patients who had elevated serum creatinine level but didnt need dialysis returned to normal, while only 2 out of 8 cases who needed renal dialysis obtained recovery of serum creatinine to normal level, and 4 went on maintenance dialysis. Conclusions The clinical manifestation of ANCA-associated vasculitis is various with lung and kidney the most commonly affected organs. ANCA test and renal biopsy is helpful for early diagnosis. Aggressive treatment in time can improve renal function. There is little chance of renal recovery for advanced cases.