Radical cystectomy remains the standard treatment for intravesical Bacille Calmette-Guerin (BCG) unresponsive non-muscle invasive bladder cancer (NMIBC) because potential bladder-preserving therapies are not well established. Combination of radiotherapy with programmed death-1 (PD-1) antibody may offer an optional bladder preservation treatment for high-risk/extremely high risk NMIBC. Hence, the current study aims to investigate the safety and efficacy of short-course radiotherapy (5×5 Gy) and toripalimab (PD-1 antibody) as a novel bladder sparing treatment in this population.HOPE-04 is an open-label, single-arm, phase II study, designed to evaluate the safety and efficacy of short-course radiotherapy and toripalimab in patients with high-risk/extremely high risk NMIBC. Fifty-five patients with pathological and imaging diagnosed NMIBC with or without BCG treatment will be recruited. Radiotherapy of 5×5 Gy will be given to the whole bladder followed by a focal tumour bed boost and concomitant administration of toripalimab of 240 mg intravenous infusion every 21 days for 12 cycles (about 1 year). The primary endpoints are disease-free survival and safety. The secondary endpoint is overall survival. Additional indicators include implementation rate of salvage surgery and quality of life.This trial has been approved by the Ethics Committee of West China Hospital, Sichuan University. Trial findings will be disseminated via peer reviewed journals and conference presentations.Chinese Ethics Committee of Registering Clinical Trials (ChiCTR2200059970).© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.