Background: Total hip arthroplasty and total knee arthroplasty are widely performed worldwide. Patients undergoing total hip or knee arthroplasty are often discharged after a short hospital stay. Using information and communication technologies, such as mobile applications, to provide rehabilitation services remotely may be a strategy to support patients' postoperative recovery., Objective: This study aimed to evaluate the effectiveness of a rehabilitation programme delivered via a mobile application among Chinese patients after total hip or knee arthroplasty., Design: Randomised controlled trial., Setting: A teaching hospital in Shanghai, China., Participants: Eighty-six patients who received a unilateral primary total hip or knee arthroplasty., Methods: The participants were recruited in the hospital and randomised into either the experimental or control group. Once discharged from the hospital, the control group (n = 43) received usual care, and the experimental group (n = 43) received usual care plus a 6-week mobile rehabilitation programme. Outcomes were assessed three times: the day before hospital discharge and 6 and 10 weeks after discharge. Primary outcomes were the changes in scores of self-efficacy and patient-reported physical function from baseline to 6 weeks post-discharge. Secondary outcomes included changes in scores of pain, depression, anxiety, and health-related quality of life. Data were analysed using generalised estimating equations., Results: At 6 weeks after hospital discharge, the experimental group showed statistically significant improvements compared to the control in scores of self-efficacy (adjusted mean difference = 0.72, 95% CI 0.31 to 1.14, P < .001) and patient-reported physical function (adjusted mean difference = 4.57, 95% CI 1.24 to 7.90, P = .007). The between-group difference in self-efficacy probably reached clinical significance. At week-10 follow-up, the experimental group had statistically significant improvements in scores of self-efficacy (adjusted mean difference = 0.64, 95% CI 0.33 to 0.95, P < .001), health-related quality of life (adjusted mean difference = 0.06, 95% CI 0.01 to 0.10, P = .018), anxiety (adjusted mean difference = -0.51, 95% CI -0.91 to -0.10, P = .015), and depression (adjusted mean difference = -0.37, 95% CI -0.66 to -0.08, P = .012). The between-group difference in self-efficacy and health-related quality of life may be clinically significant., Conclusion: Mobile application-based rehabilitation demonstrated potentially positive effects on patients' self-efficacy, patient-reported physical function, health-related quality of life, and levels of anxiety and depression., Trial Registration: Registered with the Australian New Zealand Clinical Trials Registry on 6 July 2021 (ACTRN12621000867897)., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)