To examine the impact of hemoglobin A1c (HbA1c) criterion on the diagnosis of prediabetes in Koreans, we analyzed nationally representative cross-sectional data of 5,845 Korean adults aged ≥20 years from the Fifth Korea National Health and Nutrition Examination Survey 2011. Standardized prevalence rates of prediabetes in Korean adults by fasting plasma glucose (FPG; 5.6–6.9 mmol/L), HbA1c (5.7–6.4% [39–46 mmol/mol]), and combined criteria were 16.9, 28.4 and 33.8%, respectively. Among the subjects with prediabetes, 16% met FPG criteria only, 55% met HbA1c criteria only and 29% met both criteria. Prediabetic subjects who met HbA1c criteria only were significantly older, more likely to be women, and had lower hemoglobin and serum iron concentrations, whereas those who met FPG criteria only had higher body mass index, waist circumference, systolic and diastolic blood pressure. In conclusion, introduction of HbA1c criterion markedly increased the prevalence of prediabetes in Koreans, and the two criteria identified people with different characteristics.