No studies have reported changes in self-care behavior, and it remains unclear whether Free Style Libre (Libre) differs from conventional blood glucose self-monitoring devices in this regard. Therefore, we instructed diabetes patients using conventional self-monitoring blood glucose (SMBG) devices to use the Libre and prospectively examined the effect of this new device on self-care behavior and patient treatment satisfaction. The subjects comprised 41 outpatients with diabetes who were using conventional SMBG devices. The subjects were randomly assigned to group A, which comprised patients using Libre for ≥2 weeks (n = 21), or group B, which comprised patients who continued using conventional SMBG devices (n = 20). All patients received 30 minutes of diet and exercise therapy instruction from a registered dietitian and nurse (or clinical laboratory technologists). The Summary of Diabetes Self-Care Activities measure (SDSCA) was administered at baseline, 1, 3, and 6 months. Changes in the SDSCA, glycated hemoglobin (HbA1c), glycated albumin (GA), and body weight from baseline to 1 month were analyzed (UMIN000029016). At baseline, the two groups did not differ significantly in terms of the HbA1c, GA, body weight, or 17 SDSCA items. At 1 month, the numbers of days involving eating five or more servings of fruits and vegetables were 5.0 (3.3, 6.8) in group A and 3.0 (1.0, 6.0) in group B, the numbers of days involving exercise for at least 30 minutes were 5.0 (2.0, 6.0) in group A and 2.0 (0, 3.0) in group B, and the number of days involving specific exercise were 3.0 (2.0, 6.0) in group A and 1.5 (0, 2.3) in group B; both of these values were significantly higher in group A than in group B (p = 0.033, 0.037 and 0.041, respectively). These results suggest that the use of the Libre may improve the self-care behaviors of diabetes patients regarding diet and exercise, compared with the use of conventional SMBG devices. Disclosure A. Kudara: None. T. Tosaki: Other Relationship; Self; Eli Lilly and Company, Takeda Development Center Asia, Pte. Ltd., MSD K.K., Mitsubishi Tanabe Pharma Corporation. S. Sato: None. A. Inagaki: None. M. Kondo: None. S. Tsunekawa: None. Y. Kato: Speaker's Bureau; Self; Merck Sharp & Dohme Corp., Sanofi, Takeda Pharmaceutical Company, Eli Lilly Japan. H. Kamiya: Other Relationship; Self; MSD K.K., Ono Pharmaceutical Co., Ltd., Sanofi K.K., AstraZeneca, Astellas Pharma KK, Eli Lilly and Company, Novartis Pharma K.K., Dainippon Sumitomo Pharma Co., Ltd, Boehringer Ingelheim Pharmaceuticals, Inc., Takeda Pharmaceutical Co., Ltd, Ono Pharmaceutical Co., Ltd. J. Nakamura: Other Relationship; Self; Astellas Pharma US, Inc., AstraZeneca, Ono Pharmaceutical Co., Ltd., MSD K.K., Kyowa Hakko Kirin Co., Ltd., Kowa Pharmaceuticals America, Inc., Sanofi K.K., Taisho Pharmaceutical Co., Ltd., Takeda Development Center Asia, Pte. Ltd., Mitsubishi Tanabe Pharma Corporation, Eli Lilly and Company, Novartis Pharma K.K., Pfizer Inc..