Objective: To examine the association between serum vitamin D level and thyroid function indicators among elderly patients with type 2 diabetes mellitus (T2DM), so as to provide the evidence for the prevention and treatment of thyroid function abnormality among elderly patients with T2DM. Methods: Inpatients aged 60 years and older and admitted to the department of endocrinology of Zhejiang Hospital were selected as the study subjects. Gender, age, course of disease and other basic information were collected through questionnaire surveys. The serum 25-hydroxyvitamin D[25-(OH) D], thyroid stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (TT3), and total thyroxine (TT4) were measured. The correlation between serum vitamin D level and thyroid function indicators in elderly patients with T2DM was evaluated by a multiple linear regression model. Results: A total of 402 elderly patients with T2DM were surveyed, including 210 males (52.24%) and 192 females (47.76%), and had a median age of 70.00 (interquartile range, 12.00) years and a median course of disease of 14.00 (interquartile range, 14.00) years. There were 162 patients with insufficiency of vitamin D (40.30%) and 182 patients with deficiency (45.27%). The levels of TSH and glycated hemoglobin in the vitamin D deficiency group were (2.34±1.66) μIU/mL and (8.83±2.14) %, respectively, which were higher than those in the normal group [(1.74±1.10) μIU/mL and (8.11±1.75) %; P<0.05]. The levels of FT3 and FT3/FT4 in the vitamin D deficiency group were (2.86±0.48) μIU/mL and 2.85±0.71, respectively, which were lower than those in the vitamin D insufficiency group [(3.09±0.47) pg/mL and 3.14±0.81, P<0.05]. Multiple linear regression analysis showed a negative correlation between 25- (OH) D and TSH (β'=-0.159, P=0.001). Conclusion The vitamin D deficiency may be associated with the increase of TSH level among the elderly patients with T2DM.