Purpose: To investigate whether the relationship between body mass index (BMI) and incident diabetes is modified by different alanine or aspartate aminotransferases (ALT or AST) levels. Methods: We carried out an analysis of 6484 participants aged 40 years or older using data from the Korean Genome Epidemiology Study. The serum aminotransferase levels were stratified into low and high groups according to the median values and classified into three groups: both low, either high, and both high. To assess the association between BMI and incident diabetes according to the serum aminotransferase levels, multiple logistic regression models were used. Results: In participants with high levels of both ALT and AST, compared with the first BMI quartile, the adjusted odds ratios for incident diabetes of the second, third, and fourth BMI quartiles were 1.72 (95% confidence interval, 0.84–3.55), 2.19 (1.11–4.33), and 3.08 (1.60–5.90), respectively (P trend <.001). In participants with either high ALT or AST, the adjusted odds ratios were 3.58 (1.23–10.41), 2.65 (0.90–7.76), and 5.28 (1.86–15.02), respectively (P trend =.005). However, in participants with both low ALT and AST levels, high BMI was not independently associated with the risk of incident diabetes. Conclusions: There was a strong association between BMI and incident diabetes among individuals with high aminotransferase levels, whereas no association was observed among those with low aminotransferase levels.