Diabetes mellitus is a chronic disease that has contributed greatly to increased morbidity and mortality of millions of people both globally and in Indonesia. Acute and chronic complications can attack patients when the disease is negligible, thus it will be a very complex problem that can increase the destruction of health systems in developing countries such as Indonesia. Self-care activities in the treatment of diabetes is one factor that plays an important role and is a real change in the management of diabetes. This study aimed at determining the contribution of self-care activities on HbA1C levels in patients with diabetes mellitus type 2. The design of this research was descriptive analytic cross-sectional design. The location of research was done by using purposive sampling at the Puskesmas in South Denpasar. Sampling was carried out by Proportion Stratified Random Sampling technique, to obtain a total sample of 63 patients. The method of data collection using a questionnaire which consisted of a questionnaire about the characteristics of the respondents including data HbA1C test results and questionnaire self-care activities. Results showed that all components of self-care activities significantly correlated to HbA1C levels and 41% self-care activities contributed to the levels of HbA1C (Adjusted R2 = 0.41, p <0.01). Results of this study are expected to minimize the complications of diabetes mellitus and improving the quality of life of patients with type 2 diabetes.