Background: Post orthopedic surgery patients experiencing numerous symptoms such as pain, which is the most frequently reported symptom that is linked to decreased quality of life and impaired overall function. Diaphragmatic breathing technique is an effective complementary and non-pharmacological technique used to reduce pain with beneficial effects on physical and mental health in patients post orthopedic surgeries. Aim of the study: To evaluate the effect of diaphragmatic breathing technique on pain intensity for adult patients post orthopedic surgeries. Design: A quasi-experimental design was utilized to conduct the current study. Setting: The study was conducted in orthopedic department affiliated to Benha University Hospital, Qalyubia Governorate, Egypt. Subjects: A purposive sample of sixty-five adult patients post orthopedic surgeries within six months were enrolled in this study. Tools: Four tools were used to collect data; (I) Structured interview questionnaire for patients which consisted of patients' personal and health data, (II) Patient's knowledge questionnaire, (III) Patient's practice observational checklist, (IV) The Brief Pain Inventory. Results: There was significant statistical improvement in total knowledge and practice scores of studied patients after three months of implementing the technique as compared to pre implementation, all mean total scores of pain scale for post orthopedic surgery patients decreased significantly after applying diaphragmatic breathing technique. Finally, the independent variables contributing to variance in pain score were knowledge and practice scores, as well as respiratory rate, accounting for 51.8% of the variance of pain intensity. Conclusion: Diaphragmatic breathing technique had a positive effect in decreasing pain intensity for post orthopedic surgery patients. Recommendations:  Importance of presenting posters to remind patients about diaphragmatic breathing technique and to improve patients' knowledge and practices. Also, hospitals are recommended to use the diaphragmatic breathing technique alongside other treatments to decrease pain intensity in patients post orthopedic surgeries.