We examined the effects of a lifestyle intervention program with a smartphone app augmented by intermittently scanned continuous glucose monitoring (isCGM) of persons at high risk of developing diabetes in a 12-week randomized open-label trial (UMIN00004640). The program monitored blood glucose fluctuations and lifestyle habits and displayed them in an easy-to-understand interface as well as provided personalized lifestyle intervention messages. The primary endpoint was the change in time in range (TIR) of 70-140 mg/dL between intervention (App) and control (C) groups. Among 168 patients (mean age 48.1 y, mean BMI 26.6 kg/m2, and male 80.4%), 82 and 86 were assigned to the App group and C group, respectively. After 12 weeks, TIR of 70-140 mg/dL significantly improved in the App group compared to the C group (-2.6 min/day vs. +31.5 min/day, p=0.03). Changes in time above range (>140 mg/dL; -20.9 min/day vs. -22.6 min/day, p=0.86) did not differ, whereas time below range (<70 mg/dL; +23.5 min/day vs. -8.9 min/day, p=0.02) improved in App compared to C. BMI (-0.26 vs. -0.59, p=0.017) and carbohydrate intake (-4.4 kcal/day vs. -22.7 kcal/day, p=0.049) also improved in App compared to C. Intervention with a smartphone app and isCGM increased glycemic control with a decrease in carbohydrate intake and weight loss. Disclosure M.Kitazawa: None. H.Sone: Research Support; Novo Nordisk, Astellas Pharma Inc., Kyowa Kirin Co., Ltd., Taisho Pharmaceutical Holdings Co., Ltd., Ono Pharmaceutical Co., Ltd., Eisai Co., Ltd., Takeda Pharmaceutical Co., Ltd. H.Suzuki: None. C.Horikawa: None. Y.Takeda: None. I.Ikeda: None. M.Hatta: None. M.Iwanaga: None. T.Yamada: None. K.Fujihara: None.