Background: Laparoscopic sleeve gastrectomy surgery was viewed as an effective therapy for morbid obesity. The lifestyle of obese patients must be changed to complete surgery success and sustain a permanent loss of weight without recurrence. Objectives: To evaluate the effect of an instructional guide on lifestyle modification for morbidly obese patients undergoing sleeve gastrectomy surgery at Zagazig University Hospitals. Method: An interventional study was conducted at outpatients' clinic for obesity at Zagazig University Hospitals in stages that included assessment of patients' knowledge regarding lifestyle modification after laparoscopic sleeve gastrectomy surgery. All patients were clinically examined, investigations were done. Then applying a health education program about lifestyle modification after laparoscopic sleeve gastrectomy surgery. Reassessment of patients' knowledge about lifestyle modification following laparoscopic sleeve gastrectomy surgery, re-examining all patients post-operatively to evaluate the intervention. The post-operative assessments: 1-month post-surgery, 6 months post-surgery and 12 months post-surgery were done. Results: A total sample of 38 patients with a mean age 34.6 ± 5.7 years. Thirty-nine (39) co-morbidities were identified among them, 56.4% of them were resolved. The majority of patients (94.8%) had unsatisfactory knowledge regarding lifestyle modification after laparoscopic sleeve gastrectomy surgery before applying health education program, while after applying health education program the patients' knowledge was satisfactory (81.6%). Laparoscopic sleeve gastrectomy accompanied by lifestyle modification achieved a marked reduction in body weight and body mass index. Conclusion: Lifestyle modification has an additive role in weight loss with surgical intervention.