Objectives:The aims of this study were to examine changes of cognitive function and its characteristics, and to identify influencing factors on cognitive fuction in patients with thyroid disorders. Methods:Data of 98 patients with thyroid disorders(16 males and 82 females) recruited from thyroid clinic in the Endocine Center of Kosin University Gospel Hospital were obtained by semi-structred interviews and MoCA-K(Korean Version of the Montreal Cognitive Assessment) and Korean version of the HDRS-17(Hamilton Depression Rating Scale-17). Results:1) The cognitive dysfunction was seen in 24 patients with thyroid disorders(24.49%). The total scores of the MoCA-K tests in thyroid patients with cognitive dysfunction(18.42±3.75) were significantly(p<0.001) lower than those of controls(26.43±2.01). Their subtest scores of the MoCA-K such as visuospatial/executive, naming, attention, language, abstraction, delayed recall were also lower than those of controls. 2) The thyroid patients with MoCA-K ≤22 showed higher age and onset age of thyroid disorders, and had lower education and HDL-cholesterol(p<0.001 respectively). 3) Total scores of the MoCA-K tests in patients with thyroid disorders had positive correlation with education(ρ=0.583, p<0.01), and had negative correlation with age(ρ=-0.462, p<0.01) and onset age of thyroid disorders(ρ=-0.494, p<0.01). Otherwise, triiodothyronine and HDL-cholesterol had positive correlation, and sex and triglyceride had negative correlation with some subtest scores of the MoCA-K. Conclusions:The cognitive dysfunction accompanied in about 1/4 of patients with thyroid disorders. The finding that the cognitive function in thyroid disorders seemed to be mainly associated with age and onset age of thyroid disorders, suggested a possibility of an important role of aging mechanism.