Abstract Background Although rehabilitation is recommended for terminal cancer patients, the specific components and methods of such programs are poorly documented. No studies to date have examined the effectiveness of rehabilitation for terminal cancer patients. This study aims to evaluate the efficacy of a new intervention for rehabilitation therapists, using the Op-reha Guide (Guide to Optimal and Patient-Centred Rehabilitation Practice for Patients in Palliative Care Units [PCUs]) in rehabilitation practice. This guide consists of recommended actions and attitudes for rehabilitation therapists and aims to optimise therapists’ actions according to the patient’s needs and condition. It shares goals with terminal cancer patients to maintain their activities of daily living (ADL). Methods This study uses a multicentre, prospective, randomised controlled trial (RCT) design with two parallel groups in PCUs where specialised rehabilitation will be routinely performed for terminal cancer patients by rehabilitation therapists. Participants will be randomised (1:1) to intervention (the Op-reha Guide) and control groups (usual rehabilitation). We will then conduct an observational study in PCUs that do not perform specialised rehabilitation for terminal cancer patients; this will be considered the usual care group, and the efficacy of usual rehabilitation will be quantitatively evaluated. Inclusion criteria are hospitalisation in PCU, European Cooperative Oncology Group Performance Status of 2 or 3, and clinical estimation of life expectancy of 3 weeks or more. Patients with severe symptom burden will be excluded. We hypothesise that the Op-reha Guide will be more effective in maintaining the ADL of terminal cancer patients hospitalised in PCUs than usual rehabilitation. The primary endpoint is defined as the change in (total) modified Barthel Index from baseline to Day 22. Quality of life will be a secondary endpoint. In total, 135 patients will be recruited from 16 Japanese sites between July 2019 and December 2021. Discussion This will be the first trial to evaluate the efficacy of specialised rehabilitation for terminal cancer patients hospitalised in PCUs, and will contribute to the evidence on the efficacy of implementing rehabilitation for terminal cancer patients. Trial registration UMIN-CTR, UMIN000037298 R000042525 (date of registration 7 July 2019).