Abstract Background: The increasing number of smartphone application users in the community can be used as a new breakthrough in providing solutions to provide interventions. As the example in Educating Type-2 Diabetes Mellitus (T2DM) patients using the Contextual Teaching and Learning (CTL) model to reduce blood glucose and improve self-care at an affordable cost. This study aims to determine the effect of smartphone application education on self-care and blood glucose levels in T2DM patients with the CTL model. Methods: This study was a randomized controlled study pre-test and post-test design conducted on T2DM patients attending nine health centers in Kediri City, Indonesia. The research was on October 2, 2023 - January 2, 2024 by 131 intervention group and 131 control group. Result: Mean reduction in blood glucose levels in T2DM patients using the CTL model smartphone application pre-test was (158.7±17.4), post-test was (107.5±6.5) with a P-Value of 0.000. Mean self-care pre-test was (43.03±1.62) and post-test was (81.53±5.32) with a P-Value of 0.000. Domains of blood sugar monitoring, exercise, diet, foot care with blood glucose levels P-Value (0.028±0.000±0.002±0.182). Conclusions: There is an overall effect of smartphone applications in the CTL model on blood glucose levels and self-care in T2DM patients. There is an influencing effect of monitoring blood glucose level, exercise, and diet control on blood glucose level. Foot care does not affect blood glucose levels.