Recently, mobile health care has been applied to manage diabetes requiring self-management. Health care by mobile applications (apps) has a great advantage when applied to patients with diabetes; the adherence to self-management activities for diabetes can be improved through mobile apps. The Food and Drug Administration (FDA) has cleared and approved the use of some mobile apps as medical devices for the management of diabetes since 2010. However, mobile apps may not be effective for all patients. We here report the effect of use of mobile-based diabetes care app (Healthy-note app) for 2 patients with diabetes, and discuss issues and strategies for effective mobile intervention. Further study is needed on improving patient's participation to increase the effect of management via a mobile app.