Objective: This research is purposed to validate the utility of smartphone based glucose monitoring system in the private clinic setting· Methods: In this multicenter, cluster-randomized and prospective study, we enrolled the 13 private clinics in Seoul and other local large cities· 150 subjects from 9 institutions and 97 subjects from 4 institutions were assigned to intervention and control group, respectively· The intervention group was monitored by smartphone· When patient checked the glucose level and inputted the results into the smartphone, and then the smartphone transmitted the data to the main server· Every week, the doctor checked the patient’s glucose results and sent the feed-back massage· The control group received the general lifestyle modification education and out-patient clinic consultation every month· After 3 months, changes from baseline in Hba1c and clinical data were evaluated· Results: At 3-month, greater reduction in mean HbA1c level was observed in the intervention group (-0·63 ± 0·82 %, p < 0·0001) compared with control group (-0·27 ± 0·71 %, p = 0·0006)· And this was greater in patient with higher baseline HbA1c level (>8·0%, intervention group; -1·06 ± 0·82%, p < 0·001 vs· control group; -0·25 ± 0·82 %, p = 0·1692)· Fasting plasma glucose (FPG) was also significantly reduced in the intervention group (-18·86 ± 63·35 mg/dL, p < 0·0001) compared with control group (-2·33 ± 53·67 mg/dL)· In addition, significant reduction was observed in diastolic BP, body weight· Conclusion: Smartphone based glucose monitoring and feed-back system was effective when applied to the private clinic setting· Even the general doctor could effectively utilize this system, it could be applied to the diverse institutions and patients·