BACKGROUND: The preservation of islet β-cell function in elderly patients with type 2 diabetes mellitus (T2DM) is a top priority for diabetic control. AIM: To assess the preservation of islet β-cell function among elderly Chinese patients with T2DM after different anti-diabetic treatments. METHODS: In this longitudinal observational study, elderly patients with T2DM treated with insulin, oral antidiabetic drugs or a combination of both were enrolled to disclose their islet β-cell function between baseline and follow-up. Islet β-cell function was determined by the plasma Homeostasis Model for β-cell function (HOMA-β), C-peptide and area under the curve (AUC) based on oral glucose tolerance test. Changes in β-cell function (decrement or increment from baseline) between different therapy groups were the outcomes. RESULTS: In total, 745 elderly patients (≥ 60 years) with T2DM [insulin monotherapy, CONCLUSION: In Chinese elderly patients with T2DM, islet β-cell function progressively declines regardless of insulin supplement or insulin plus OAD treatments.