Background: Bariatric/metabolic surgery is a valid treatment option for patients with obesity, type 2 diabetes (T2DM) and nonalcoholic fatty liver disease (NAFLD) . Although magnetic resonance imaging (MRI) is more accurate, the evaluation of NAFLD is generally limited to ultrasonography and various scoring systems. Here, we show a therapeutic effect of laparoscopic sleeve gastrectomy (LSG) on NAFLD in Japanese patients with T2DM using MRI. Methods: We conducted a prospective observational study of Japanese patients with obesity, T2DM, and NAFLD over 1 year (UMIN000034667) . The participants were 20 surgically (LSG group) and 20 medically (control group) treated patients. We compared various parameters at baseline and 1 year later in the two groups. The primary outcome was the change in the MRI proton density fat fraction and elasticity of the liver. The secondary outcomes were changes in metabolic parameters, including body mass index (BMI) , HbA1c, and diabetic remission rate. Results: To date, 28 patients (LSG 15, control 13) have completed the study. Their baseline BMIs were LSG 39.5 [35.5, 45.1] kg/m2 and control 35.9 [32.6, 43.6] kg/m2 (P=0.12) . One year after surgery, the index of hepatic steatosis, MRI proton density fat fraction (LSG −13.3±8.4%, control −0.8±5.5%, P<0.01) , was significantly lower in the LSG group. A second index, stiffness on MRI elastography (LSG −0.2 [−0.3, 0.1] kPa, control −0.[−0.35, 0.4] kPa, P=0.60) tended to be lower. In addition, BMI (LSG −9.5±3.2 kg/m2, control −0.1±0.6 kg/m2; P<0.01) and HbA1c (LSG −1.4±1.0%, control 0.3±0.8 kg/m2; P<0.01) were significantly lower. The postoperative diabetic remission rate was 86.7%. Conclusion: We have shown that LSG causes marked weight loss and diabetic remission in many patients. NAFLD was also markedly ameliorated, especially hepatic steatosis, although a longer study may be required to detect an improvement in fibrosis. Disclosure Y.Oe: None. T.Atsumi: Consultant; AbbVie Inc., AstraZeneca, MEDICAL & BIOLOGICAL LABORATORIES CO., Nippon Boehringer Ingelheim Co. Ltd., Novartis Pharma K.K., Ono Pharmaceutical Co., Ltd., Pfizer Inc., Research Support; AbbVie Inc., Alexion Pharmaceuticals, Inc., Astellas Pharma Inc., Chugai Pharmaceutical Co., Ltd., Daiichi Sankyo, Mitsubishi Tanabe Pharma Corporation, Nippon Boehringer Ingelheim Co. Ltd., Otsuka Pharmaceutical Co., Ltd., Pfizer Inc., Taiho Pharmaceutical Co. Ltd., Takeda Pharmaceutical Company Limited, Teijin Pharma Limited, Speaker's Bureau; AbbVie Inc., Astellas Pharma Inc., Bristol-Myers Squibb Company, Chugai Pharmaceutical Co., Ltd., Daiichi Sankyo, Eisai Co., Ltd., Eli Lilly and Company, Kyowa Kirin Co., Ltd., Mitsubishi Tanabe Pharma Corporation, Novartis Pharma K.K., Pfizer Inc., Taiho Pharmaceutical Co. Ltd., Takeda Pharmaceutical Company Limited, UCB, Inc. H.Miyoshi: Research Support; Abbott Japan Co., Ltd., Boehringer Ingelheim International GmbH, Daiichi Sankyo, Kowa Company, Ltd., LifeScan, Mitsubishi Tanabe Pharma Corporation, Novo Nordisk, Ono Pharmaceutical Co., Ltd., Sumitomo Dainippon Pharma Co., Ltd., Taisho Pharmaceutical Holdings Co., Ltd., Speaker's Bureau; Astellas Pharma Inc., Boehringer Ingelheim International GmbH, Eli Lilly and Company, Kowa Company, Ltd., Merck & Co., Inc., Mitsubishi Tanabe Pharma Corporation, Novo Nordisk, Ono Pharmaceutical Co., Ltd., Sanofi K.K., Sumitomo Dainippon Pharma Co., Ltd., Taisho Pharmaceutical Holdings Co., Ltd. T.Takase: None. K.Cho: None. K.Ogawa: None. Y.Ebihara: None. A.Miya: None. H.Nomoto: None. H.Kameda: None. A.Nakamura: Research Support; Kissei Pharmaceutical Co., Ltd., MSD, Nippon Boehringer Ingelheim, Taisho Pharmaceutical Holdings Co., Ltd.