Background: Takayasu arteritis (TAK) is an immune-induced granulomatous vasculitis that occurs primarily in young Asian women. Our previous cohort studies have indicated that leflunomide (LEF), which can lead to rapid induction and might be a promising alternative treatment for TAK. Objectives: To compare the efficacy and safety of LEF versus placebo combined with prednisone for active TAK in a Chinese population. Design: This will be a multicenter, randomized, double-blinded controlled trial aiming to recruit 116 TAK patients with active disease. This study will last 52 weeks. Methods and analysis: Participants will be assigned randomly to the LEF intervention arm or placebo control arm at a 1:1 ratio. Initially, LEF combined with prednisone will be given to the intervention arm and a placebo tablet combined with prednisone will be given to the placebo arm. At the end of week 24, subjects who achieved clinical remission or partial clinical remission will proceed to maintenance therapy with LEF to the end of week 52; those who did not achieve clinical remission or partial clinical remission in the LEF intervention arm will drop out from the study, and those in the placebo control arm will switch to LEF treatment to week 52. The primary endpoint will be the clinical remission rate of LEF versus placebo at the end of week 24. The secondary endpoints will be the time to clinical remission, mean dose of prednisone, disease recurrence, time to recurrence, adverse events, as well as clinical remission in subjects who switched from the placebo control arm to LEF therapy after week 24. Intention to treat will be the primary analysis. Discussion: This is the first randomized double-blinded placebo-controlled trial to clarify the efficacy and safety of LEF in treating active TAK. The results will provide more evidence for TAK management. Registration: ClinicalTrials.gov identifier: NCT02981979.