Objectives: This study was conducted to determine factors related to glycemic control among Korean patients with diabetes. Methods: Data was collected from the Fourth (2007-2009) Korea National Health and Nutrition Examination Survey (KNHANES) which was a nationwide, cross-sectional survey. The study participants who are available for hemoglobin A1c (HbA1c) were 1,441 patients with diabetes aged 30 years and older. Poor glycemic control was defined as $HbA1c{geq}7.0%$. Data were analysed using logistic regression. Results: The proportion of patients with the poor glycemic control ($HbA1c{geq}7.0%$) was 49.5%. After adjusting for confounding factors, younger aged persons (30-49 years) were less likely to control the blood glucose than older aged persons (60-69 years) (Adjusted OR=0.533, 95% CI [0.295-0.960]) and longer duration of diabetes was positively related to poor glycemic control (Adjusted OR=2.018, 95% CI [1.418-2.873]). Conclusions: Age and duration of diabetes were significantly related to blood glucose control. Therefore, considering these factors is helpful for developing a strategy to improve blood glucose control in diabetes.