Case Study: A 78-year-old man with a history of diabetes, hypertension received the third dose of Pfizer-BioNTech COVID-19 vaccine and complained of dyspnea and leg edema. Medication included sitagliptin, metformin, valsartan. His serum creatinine and serum urea nitrogen were 3.30 mg/dL and 67.7 mg/dL, respectively. His potassium was 6.7 mmol/L, and bicarbonate was 15.7 mmol/L. Urinalysis showed hematuria(3+) and urine protein to creatinine ratio(uPCR) was 2.618 mg/mg. Computed tomography of abdomen showed no acute abnormality. Polymerase charin reaction testing for SARS-CoV-2 was negative. ANCA immunofluorescence titer was 1:40(reference range of <1:20), with elevated MPO-ANCA level 42U/mL(reference range 3.5~5.0U/mL). Other serologic tests including complement levels were unremarkable. Kidney biopsy revealed focal necrotizing and extracapillary proliferative glomerulonephritis, consistent with ANCA-associated glomerulonephritis. He was diagnosed with ANCA-assiciated vasculitis(AAV). Immediate steroid pulse therapy(1mg/kg) was started, followed by intravenous cyclophosphamide. Despite immunosuppressive treatment, serum creatinine and urea nitrogen rose up to 5.15 mg/dL and 98.6 mg/dL, respectively and edema worsened. Hemodialysis and plasma exchange were started. On the 13th day of hospitalization, the patient complained of leg pain and duplex sonography showed thrombosis at right soleal vein, left small saphenous vein, and left soleal vein. Apixaban was started and symptom improved afterwards. After 1-month-follow up, despite immunosuppressive treatment, hemodialysis, and plasma pheresis, patient’s renal function did not recovered and required maintenance dialysis. As vaccines being administered for COVID-19, adverse reactions such as glomerulonephritis have also been reported. This is a case of new onset AAV and DVT after COVID-19 vaccination. Because there are no other factors that can cause acute kidney injury and DVT, we suppose vaccination might cause AAV and DVT. Previous studies suggested vaccines such as viral RNA-based vaccines might increase ANCA production. Although this case cannot determine conclusive relationship between COVID-19 vaccination and AAV with DVT, ongoing surveillance for similar complications is prudent.