Objective: Lifestyle is an important element of diabetes management. However, lifestyle is made up of various components which are rarely measured objectively. We aimed to define healthy lifestyle related to glycemic control based on activity tracker in type 2 diabetes mellitus (T2DM). Methods: We performed a prospective observational study on 24 patients with T2DM who aged 30 to 60 years. Patients were educated to wear an activity tracker Fitbit on their wrist for three months so that continuous data such as physical activity, sleep, and heart rate were collected. Expectation- maximization (EM) cluster analyses were performed for group clustering. Metabolic parameters including glycated hemoglobin (HbA1c) was measured at baseline and end of the study. Results: Mean age of participants was 46.8 years. EM clustering analysis produced only two groups; ‘group A (n=9)’ and ‘group B (n=15)’. Subjects in group A had seemingly healthier lifestyle based on activity tracker measures compared to those in group B. They had longer sleep length (6.5 vs.5.2 hours), lower deviations of sleep onset and awake (3.3 vs. 6.7, 2.3 vs. 4.4, respectively), higher daily steps counts (11950.5 vs 6255.4 steps) and lower resting heart rate (75.2 vs. 82.4 per min). The SHAP summary plot analysis indicated circadian rhythm-related factors were major determinants of the clustering. Healthy lifestyle cluster (group A) indicated lower proportion shift works, lower body mass index (25.4 vs. 29.5 kg/m2) and longer duration of diabetes (11.9 vs. 5.7 years) than unhealthy cluster (group B). Mean HbA1c level was 0.2% lower at baseline in healthy cluster and 0.3% lower at the end of follow-up than unhealthy cluster. Conclusion: Clustering based on activity tracker distinguished healthy lifestyle from unhealthy one, which was related to glycemic control in T2DM. Factors related to sleep or circadian rhythm were major determinants of the lifestyle clustering.