Background Avacopan, a complement C5a receptor antagonist, has been proven effective in treating ANCA-associated vasculitis. Since 2021, it has been globally approved and widely used. In Korea, avacopan received regulatory approval in September 2023, but its clinical effects in the Korean population remain unclear. To address this gap, we report four cases of ANCA-associated vasculitis presenting with acute glomerulonephritis and acute kidney injury. Method: Avacopan has been administered to four patients through a patient support program. We retrospectively reviewed their clinical courses, focusing on renal function, proteinuria, and treatment response to avacopan in combination with conventional immunosuppression. Results Four patients (three men, one woman, aged 60–70) with rapidly progressive renal dysfunction were enrolled. Two were diagnosed with microscopic polyangiitis (MPA) and two with granulomatosis with polyangiitis (GPA). Baseline eGFR was 7 and 9mL/min/1.73m² in MPA cases and 32 and 33mL/min/1.73m² in GPA cases. Initial urine protein-to-creatinine ratios (UPCR) were 1.4, 1.2, 1.1, and 2.0g/g, respectively. One MPA patient required immediate hemodialysis (HD) due to severe uremic symptoms. Initial induction included intravenous pulse steroids with rituximab (3 cases) and cyclophosphamide (1 case). Avacopan was introduced 14–28 days after induction therapy. With avacopan use, steroids were tapered off within 2–4 months during maintenance treatment. Proteinuria improved in all three patients without dialysis, with complete resolution by three months in two cases (1 MPA, 1 GPA) and by six months in one GPA case One MPA patient’s eGFR improved (9→16), and others remained stable. The MPA patient on HD showed slow recovery of renal function, allowing dialysis tapering. Conclusions In this first Korean case series, avacopan was well tolerated without safety concerns. It enabled early steroid withdrawal, after which proteinuria reduction and renal function stabilization were maintained. Further studies are needed to assess the direct efficacy of avacopan.