Objective To observe the incidence of thyroid dysfunction in the elderly patients with type 2 diabetes mellitus (T2DM) and investigate the influencing factors. Methods A total of 190 T2DM patients (over 60 years old) without history of thyroid diseases hospitalized in our department from October 2014 to May 2015 were enrolled in this study. Their clinical and pathological data were retrospectively reviewed and analyzed. Results (1) The incidence of thyroid dysfunction was 38.4% (73/190), including 22.1% (42 cases) of low T3 syndrome and 15.8% (30 cases) of idiopathic hypothyroidism. (2) The patients with low T3 syndrome had higher level of HbA1c, older age and longer T2DM duration when compared to idiopathic hypothyroidism group and those without thyroid dysfunction (P＜0.05). The positive percentages of thyroglobulin antibody (TGAb) and/or thyroid peroxidase antibody (TPOAb) were obviously higher (70%) in hypothyroidism group (P＜0.05). (3) The 25-hydroxy vitamin D (25-OH-vit D) level was deficient among the 3 groups. (4) Logistic regression analysis showed that age was positively correlated with the incidence of low T3 syndrome (OR＝2.77, P＝0.012), and the levels of TGAb (OR＝3.57, P＝0.026) and TPOAb (OR＝4.13, P＝0.026) were respectively correlated with hypothyroidism. Conclusion Thyroid dysfunction is quite common in the elderly with T2DM, and their autoimmune background may induce hypothyroidism. Elderly patients are more likely to suffer from low T3 syndrome. But there is no difference in vitamin D deficiency among those without thyroid dysfunction, hypothyroidism and low T3 syndrome.