Objective We examined correlation between patients' own assessments of their diabetes self-management and actual glycemic control status and investigated what is the key determinants of diabetes self-care. Methods We carried a survey from patients with type 2 diabetes who had not been changed antidiabetic medications during last 6 months through questionnaires included patient's expectation of their blood glucose change and a five item scale assessing the patients' diabetes self-management (diet, exercise, blood glucose testing, foot care and medication use). We obtained their HbA1c of 2~4 months ago and that of the time of survey. Results The patient's expectation of their blood glucose change corresponded with their actual HbA1c change (κ=0.117, p=0.024). They considered that diet and exercise was the most important factors to control their blood glucose. However, self-care assessment score about diet or exercise was not correlated with the HbA1c change. Self-care assessment score about medication was inversely associated with the HbA1c change (r=-0.170, p=0.023). In stepwise multivariate linear regression analysis, medication score was the only statistically significant variable for HbA1c change (B=-0.117, p=0.023). The average self-care assessment score was 3.99±0.87 (7 points at maximum). The means and SDs for each self-care assessment subscale were as follows: 4.41±1.32 in diet, 3.1±1.86 in exercise, 1.9±2.31 in blood glucose testing, 4.17±1.85 in foot care, 6.59±0.77 in medication. Conclusion The patient's expectation of their blood glucose change was correlated with their actual HbA1c change. Medication was the most important factor for diabetes self-management. Effort to enhance medication adherence is warranted to improve glycemic control.