The purpose of this study was to investigate the effects of body mass index(BMI) on insulin. fasting blood sugar(FBS), and hemoglobin A1c(HbA1c). This study analyzed the data of 2015, The Sixth KNHANES, and it was included to 4554 subject over 20 years old. Data were analyzed using descriptive statistics, t-test, ANOVA, Pearson correlation coefficient and stepwise multiple regression analysis(SPSS 25.0). The major findings, BMI was positively correlated with insulin(r=0.397, p<0.001), FBS(r=0.241, p<0.001), and HbA1c(r=0.237, p<0.001). Factors affecting insulin are overweight(${\beta}=.130$, t=8.193, p<0.001), obesity(${\beta}=.390$, t=24.390, p<0.001) and age. the explanatory power is 13.1% (F=53.584, p<0.001). Factors affecting FBS were overweight(${\beta}=.072$, t=4.478, p<0.001), obesity(${\beta}=.186$, t= 11.485, p<0.001), age, the explanatory power was 10.6% (F=42.351, p<0.001). Factors affecting HbA1c were overweight(${\beta}=.059$, t=3.712, p<0.001), obesity(${\beta}=.190$, t=11.895, p<0.001) age and sex, the explanatory power is 14.1% (F=58.134, p<0.001). Based on this study result, diabetes mellitus prevention and management programs should include interventions related to obesity.