Disclosed is an agent for preventing/treating ANCA-related vasculitis and/or preventing the recurrence of ANCA-related vasculitis. Also disclosed is a therapeutic method using the agent. Specifically disclosed is a pharmaceutical composition comprising at least one member selected from the group consisting of eicosapentaenoic acid, a pharmaceutically acceptable salt thereof and an ester thereof as an active ingredient. The pharmaceutical composition is useful for the prevention of recurrence of ANCA-related vasculitis, the treatment of chronic ANCA-related vasculitis, and the prevention and treatment of rapidly progressive glomerulonephritis (RPGN).
