Objectives: To assess glucagon-like peptide 1 (GLP-1) secretion after oral glucose tolerance tests (OGTTs) in subjects with newly diagnosed type 2 diabetes mellitus (T2DM), impaired glucose tolerance (IGT), and normal glucose tolerance (NGT) to clarify changes in GLP-1 secretion during the course of T2DM. Methods: In this cross sectional study, 80 subjects were divided into the NGT, IGT, and T2DM groups after undergoing a 75 g OGTT from March to December 2014 at the School of Medicine, First Affiliated Hospital, Shihezi University, Xinjiang, China. Plasma total GLP-1 was measured at 0, 30, 60, 120, and 180 minutes. Homeostasis model assessment of insulin resistance (HOMA-IR), islet beta-cell function (HOMA-beta), Gutt index, Matsuda index, incremental GLP-1 (Delta GLP-1), and areas under the curves of GLP-1 (AUC(glp-1)), glucose (AUC(g)), and insulin (AUC(ins)) were calculated. Results: Plasma total GLP-1 at 30-120 minutes and Delta GLP-1 at 30-120 minutes were lower in the T2DM group than in the IGT and NGT groups (p<0.05). Peak GLP-1 levels were 35% lower in the T2DM group than in the NGT group. Plasma total GLP-1, Delta GLP1, and AUC(glp-1) correlated negatively with HOMA-IR and AUC(g), and positively with HOMA-beta, Gutt index, Matsuda index, and AUC(ins) (p<0.05). Conclusion: The GLP-1 secretion after 75 g OGTT was impaired in newly diagnosed T2DM patients, inversely proportional to IR and hyperglycemia, and positively correlated with beta-cell function and insulin sensitivity.