Objective To determine the thyroid hormone concentrations in preschool children in the Kasin-Beck disease (KBD) endemic area so as to explore the etiology of KBD. Methods Children of 1-6 years old in Naidang village,Jinchuan county, Sichuan Province, China were included. Physical examination was performed, personal history and medical history were collected, and blood samples were drawn for the determination of thyroid hormones. Results Blood samples were successfully collected from 14 children. Of them, 57.14% showed decreased TT3 levels, and 85.71% demonstrated decreased FT3 levels. All children showed significantly lower TT3 and FT3 average levels than the reference average value (P lt;0.000 01). The TT4, FT4and TSH levels were within the normal range. Conclusion Most children in the KBD endemic area showed lower T3 levels, which may act as a key factor for cartilage hypogenesis. It is suggested that a decreased TT3 level be one of the indicators for the assessment of KBD preventative effect, early monitoring and diagnosis of preclinical or subclinical stage of KBD.