This study aimed to investigate the association of Apolipoprotein B (ApoB) with the risk of diabetes in Koreans. Korean men (n = 790, 40-79 years) who had been never diagnosed for diabetes before participating were enrolled. Subjects were categorized into normal fasting glucose (NFG, n = 519), impaired fasting glucose (IFG, n = 188) and newly-onset diabetes (n = 83) according to fasting glucose levels. Age was not significantly different among the subgroups. Mean values of BMI, waist circumference, Blood pressure(BP), triglyceride, non-HDL cholesterol were significantly higher in IFG or newly-onset diabetic subjects compared to NFG subjects. The levels of glucose, insulin, free fatty acid, insulin resistance and ApoB were highest in diabetic patients and lowest in NFG subjects. According to ApoB level, subjects were divided into two groups (high-ApoB group: ≥ 87.0 mg/dL vs. low-ApoB group: < 87.0 mg/dL). The risk of diabetes was higher in the high-ApoB group than the low-ApoB group [OR₀: 2.392, (95% CI: 1.470-3.893), P₀ < 0.001]. This association was maintained after adjusted for age and BMI [OR₁: 2.228, (95% CI: 1.362-3.646), P₁ = 0.001] and further adjustment for blood pressure, triglyceride, HDL-cholesterol, LDL-cholesterol, non-HDL-cholesterol, ApoA1 and adiponectin [OR₂: 1.984, (95% CI: 1.001-4.064), P₂ = 0.049]. The association was much greater in subjects with metabolic syndrome (MetS) [OR₁: 2.805 (95% CI: 1.137-5.737), P₁ = 0.005] than in those without [OR₁: 1.917 (95% CI: 0.989-3.718), P₁ = 0.054]. After 3-month, further investigation was randomly performed in subjects with NFG or IFG who agreed to reinvestigation. Multiple stepwise regression analysis revealed that net change of ApoB levels was a main contributor to the net change of glucose levels (standardized b-coefficient: 0.315, p = 0.002). In conclusion, ApoB levels are closely associated with the increased risk of diabetes in Korean men.