Objective NAG-1 (NSAID induced gene-1) is a protein that belongs to the transforming growth factor beta superfamily. The putative role of NAG-1 might be a stress and inflammatory response cytokine. As the inflammatory response contributes to the development of type 2 diabetes mellitus (T2DM), elevated serum levels of NAG-1 are associated with T2DM. T2DM is a progressive disease from normal glucose tolerance and impaired fasting glucose (IFG). So we evaluated the relationships between NAG-1 and IFG. Methods The three groups consist of normal glucose tolerance (NGT, n = 137), IFG (n = 32) and T2DM (n = 75). We used fasting blood glucose and 75 g oral glucose tolerance test to identify the IFG from non-diabetic patients. We checked the BMI, CRP, metabolic parameters and serum fasting NAG-1 Results Age, BMI, triglyceride, insulin, glucose, HOMA-IR and NAG-1 were elevated in both IFG and T2DM. HOMA-IR (1.65 ± 0.83, 2.57 ± 1.54, 4.37 ± 4.20) and NAG-1 (484.05 ± 290.94 pg/mL, 699.31 ± 478.66 pg/mL, 866.64 ± 628.10 pg/mL) were more increased in IFG and T2DM than NGT (P < 0.001). The NAG-1 (OR = 1.005, 1.002-1.007, P < 0.001) significantly differentiated the IFG and NGT independently of age, BMI and HOMA-IR. As a prediction marker of IFG by ROC curve, the cut-off values were 500 pg/mL (AUC: 0.773, sensitivity 76.5%, specificity 70%) in male and 385 pg/mL (AUC: 0.738, sensitivity 75%, specificity 62.8%) in female. Conclusion NAG-1 presents positive correlation with insulin resistance independently of age, BMI and is accentuated in IFG and T2DM. NAG-1 may be a novel biomarker to predict for IFG from non-diabetic patients.