Background & Aims: Single anastomosis sleeve ILEAL bypass (SASI) is one of the new surgical methods for morbid obese and diabetic patients. In this method, a combination of gastric sleeves and gastric bypass is performed, which has shown better results in the treatment of patients with type 2 diabetes by increasing insulin secretion from the pancreas and decreasing the body's insulin resistance. The aim of this study was to systematically evaluate the effects of this method in the treatment of morbid obesity and comorbidities. Materials & Methods: In this systematic review, PubMed, Scopus, Web of Science and Google scholar databases with English keywords of single-anastomosis sleeve ILEAL bypass, SASI, obesity, diabetes, and bariatric bypass surgery were used until October 1, 2021. Due to the novelty of this surgical procedure, there was only 7 articles. Results: In evaluating the effects of SASI surgical method in patients with morbid obesity, the results showed that fasting blood sugar, cholesterol, high-density lipoprotein, low-density lipoprotein, body mass index and hemoglobin A1C in the one-year follow-up were significantly changed (P=0. 05). Comorbidities, such as diabetes and high blood pressure, usually improved. Conclusion: SASI by-pass surgery is an effective, safe and simple method for the treatment of morbid obesity and comorbidities and has fewer nutritional side effects. The presence of two food passageways following SASI makes it possible to reduce malnutrition. It also allows the examination of digestive problems by endoscopy. . Therefore, it is an ideal way to reduce both weight and comorbidities.