Background: Rehabilitation program after Total Hip Replacement (THR) is the most important aspect of post-operative care and has been linked to improved functional outcomes. Study aim: Was to evaluate the effectiveness of rehabilitation program on functional ability among patients undergoing total hip replacement surgery. Design: A quasi experimental design was used. Setting: Study was established in orthopedic department and outpatient orthopedic clinics at Zagazig university hospitals. Sample: A purposive sample of 80 patients undergoing total hip replacement surgery, classified into two identical groups; study group and control group (40 patients for each). Tools: Five tools were utilized; Interviewing Questionnaire for patients; Practice Observational Checklist, Lower Extremity Functional Scale (LEFS), Hip Joint Exercise Checklist, and Complications Assessment Questionnaire. Results: There was a statistical significant increase in mean score of patients' knowledge and practice regarding total hip replacement surgery in study group than those in control group post program. There was a statistical significant improvement in mean score of lower extremity functional ability and performing lying and standing exercises among patients in study group than those in control group post program with highly statistical significant differences (P = 0.001). Conclusion: The rehabilitation program had a positive effect on improving patients' knowledge and practice that reflected on improving their functional ability in performing activities of daily living. Recommendations: The initiation of a rehabilitation program should commence promptly upon the patient's admission to the hospital, Rehabilitation program should be implemented on patients with THR in various settings for improving functional ability.