BACKGROUND: Total hip arthroplasty (THA) is an increasingly common treatment for older patients with hip osteoarthritis. The best strategy for a physiotherapy intervention for older people after THA is not clear in the literature. The purpose of this protocol study is to test the feasibility of undertaking a full trial clinical to evaluate the effect of ergometer cycling-associated conventional exercises on functional results and health-related quality of life (HRQOL) of older patients with THA. METHODS/DESIGN: This study protocol is a prospective, single center, randomized controlled pilot clinical trial. Older patients (≥60 years) in the postoperative phase after primary unilateral THA for hip osteoarthritis will be consecutively recruited for this study and randomly allocated to 2 treatment groups. Group I will perform cycle ergometer and conventional exercises, and group II will perform only conventional exercises. The sessions will be conducted twice a week for 8 weeks. Assessments will be made at baseline (2 weeks postoperatively: the moment that the patients receive a referral for physical therapy, which will start after suture removal), after intervention (10 weeks postoperatively), and at 6 months of follow-up (24 weeks postoperatively). The primary outcomes are the function, evaluated using the Harris Hip Score (HHS) and the Short Physical Performance Battery (SPPB). The secondary outcome is HRQOL, measured using 2 evaluation instruments: the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Data collectors will be blinded and will not have contact with participants during the interventions. DISCUSSION: This randomized controlled trial will provide evidence regarding the effect of this exercise therapy on physical function and quality of life in older patients after THA. If our hypothesis is correct, both interventions will be effective, but the exercises on the cycle ergometer conferring better results in function, physical performance and quality of life. The study follows Consolidated Standards of Reporting Trials (CONSORT) guidelines, and the approval of the local ethics committee has been obtained. TRIAL REGISTRATION: ClinicalTrials.gov: NCT01622465 (14 June 2012).