Introduction: The effect of dipeptidyl peptidase-4 (DDP-4) inhibitors versus a-glucosidase inhibitors (AGIs) on the treatment of type 2 diabetes mellitus (T2DM) in a real-world setting is unknown. The aim of this real-world study was to compare the glucose-lowering effect and tolerability of vildagliptin as add-on to metformin monotherapy (VM) and AGI as add-on to metformin monotherapy (AM) in Chinese patients with T2DM. Methods: This was a subgroup analysis of the China Prospective Diabetes Study, a post-marketing, prospective, observational, real-world study conducted at 52 centers in China. T2DM patients with inadequate glycemic control on metformin monotherapy who received VM or AM were included. The composite primary endpoint was glycemic control (hemoglobin A1c [HbA1c] \ 7%) after 12 months in the absence of tolerability events (hypoglycemia, weight gain C 3%, or gastrointestinal events leading to treatment discontinuation). Yulong Chen, Quanmin Li and Ying Han contributed equally to this work.