Background: Most patients post-thoracic surgery complains of pain and sleep disturbances. Benson's relaxation therapy is one of the non-pharmacological pain management techniques that helps patients recover after thoracic surgery by lessening their discomfort and analgesic side effect. Aim: Evaluate the effect of Benson's relaxation therapy on pain and sleep quality among patients undergoing thoracic surgery. Design: A quasi-experimental design was utilized to conduct this study. Setting: The study was conducted at cardiothoracic surgery department in Badr University Hospital affiliated to Helwan University. Subjects: A purposive sample of 100 post-thoracic surgery patients was recruited for this study. Tools: Three tools were used for data collection I. Structured interview questionnaire included personal and health relevant data. II. Short Form McGill Pain Questionnaire (SFMPQ). III. Groningen Sleep Quality Scale (GSQS).  Results: The studied subject with mean age was 57.1 years and 55.4 years for study and control groups respectively. 78%, 66% and 74%, 66 respectively of both studied subjects were married and lived in rural areas, concerning income; around 56% of the participants hadn't enough income. While 84%and 86% of both groups respectively was having surgical history. There was an improvement in pain scores among the study group subjects at immediately postoperative day. Also there was a highly statistical significant difference existed between study and control groups regarding pain scores at 3^rd postoperative day at p< 0.001. Furthermore, there was a highly statistically significant relation between study and control groups regarding sleep quality at post-intervention period at p< 0.001 .Conclusion: Patients undergoing thoracic surgery had a positive improvement after applying Benson's relaxation technique, which reduced postoperative pain and enhanced sleep quality. Recommendation: Benson's relaxation therapy (BRT) is a simple, cost-effective, and useful tool that nurses should focus on more when caring for post-operative patients.