OBJECTIVES: Little is known about the impact of body mass index (BMI) on health-related quality of life (HRQoL) for diabetics in the Korean population. The aim of this study was to estimate the association between BMI and HRQoL of type 2 diabetic patients in Korea. METHODS: This study is a cross-sectional analysis of adults who participated in 4th (2007-2009) and 5th (2010-2011) Korean National Health and Nutritional Examination Survey(total, 42,347 participants). HRQoL was measured by EuroQoL five-dimension (EQ-5D) and its association with BMI was investigated in Korean diabetic patients, especially those who did not have adequate control of blood glucose (HbA1c ≥6.5). Multivariate linear regression was performed at p-value of 0.05 with the use of SAS software, version 9.2. RESULTS: Out of 42,347 participants, 9.04% had diagnosed of diabetes. Among 2,726 diabetic patients in Korea, we assessed the association in 1,838 patients (median age 63) whose diabetes was not adequately controlled. We found that BMI was significantly negative associated with HRQoL(-0.0038, p-value <0.001), after adjusting for age, sex, education, income, marital status, smoking status, alcohol, HbA1c, insulin treatment status, oral antidiabetic drug therapy, history of hypertension/high cholesterol/high triglyceride prevalence, stress level, and depression for more than two weeks. EQ-5D index decreased with rising BMI in Korean diabetic patients with HbA1c ≥6.5(-0.0038, p-value <0.001) CONCLUSIONS: BMI was negatively associated with HRQoL based on the multivariate regression analysis among Korean diabetic patients with HbA1c ≥6.5, after adjusting for confounding factors. This finding alerts diabetic patients to the danger of the weight gain as it is related to the lower quality of life.