INTRODUCTION: Haemophilic arthropathy, a serious complication of haemophilia, results from recurrent joint bleeding, causing progressive joint damage and severely impacting patient quality of life. Rehabilitation therapy (RT) effectively addresses declining physical function due to joint degradation, but pain during RT can hinder its success. Therefore, an effective pain-alleviating treatment method is required. The single-joint hybrid assistive limb (HAL-SJ), a powered exoskeleton, measures bioelectric potential during muscle contraction and provides motorised support, potentially alleviating pain. OBJECTIVE: This study outlines our protocol for a randomised, prospective, single-blind (evaluator) trial aimed to investigate the effects of HAL-SJ on pain reduction during RT, kinesiophobia and other physical functions in patients with haemophilia. METHODS AND ANALYSIS: This two-group comparison intervention study will include 24 male patients aged 12-85 years diagnosed with a bleeding disorder necessitating RT for pain and physical function improvement. The primary outcome measures pain changes during the first and second RT session in patients receiving HAL-SJ-assisted RT compared with traditional RT without HAL-SJ. The secondary outcomes include kinesiophobia (Japanese version of the Tampa Scale for Kinesiophobia), standing position gait (zebris FDM-T treadmill), range of motion (manual goniometer) and body surface temperature (infrared thermography camera) during the study period of up to 3 months or until the end of 10 RTs. RT intensity remains below that required to move the affected joint against gravity, given HAL-SJ's muscular support. The follow-up period extends to 1 month after the last RT. Intergroup study variables are compared by an unpaired t-test or Mann-Whitney test. Intragroup comparisons of secondary outcomes are analysed by a paired t-test or Wilcoxon signed-rank test. ETHICS AND DISSEMINATION: This study was approved by the accreditation committee of Nara Medical University Hospital. The study results will disseminate through publication in a peer-reviewed journal. TRIAL REGISTRATION NUMBER: jRCTs052220076.