Abstract: Objective：To explore the possible relationship between serum tumor marker carbohydrate antigen 19-9 (CA19-9) and pancreatic beta cell function in subjects with newly diagnosed type 2 diabetes mellitus (T2DM). Methods：A total of 118 subjects was included and evenly divided into two groups, 59 patients with newly diagnosed T2DM and 59 normal control. Two tests, 75 grams oral glucose tolerance test and insulin release test, were performed. Insulin secretion and insulin resistance were estimated by homeostasis model assessment (HOMA) beta cell function index and HOMA IR index respectively. The levels of serum CA19-9 were simultaneously determined by chemiluminescence method and other biochemical parameters were also measured. Results：Serum CA19-9 levels in T2DM group［14.48(12.05 19.30)U/mL］ were significantly higher than those in normal control group［5.03(4.37 7.38)U/mL］ (P＜0.05). The level of serum CA19-9 in glycosylated hemoglobin (HbA1c) more than 7.0% group was significantly higher than that in HbA1c less than 7.0% group and normal control group (P＜0.05 or P＜0.01). CA19-9 levels were positively correlated with total cholesterol, fasting plasma glucose (FPG), 2 hour post oral glucose tolerance test (OGTT) plasma glucose (2hPG), HbA1c, and negatively correlated with fasting insulin (FINS), HOMA-beta cell function index (P＜0.05 or P＜0.01). In multiple stepwise regression, FPG, HbA1c and HOMA beta index were significantly independent determinants for CA19-9 (P＜0.01). Conclusion：Serum CA19-9 levels increased in patients with newly diagnosed T2DM and correlated with FPG、HbA1c and HOMA-β index. CA19-9 could be served as a biological marker of pancreatic beta cell dysfunction for newly diagnosed T2DM patients.