Abstract: Objective To investigate the expression o f thyrotropin receptor (TSHR) in the extraocular muscles (EOM) of the eyes of p atients with thyroid-associated ophthalmopathy (TAO).Methods EOM specimens were obtained from 12 patients with severe TAO and 10 healthy subjects within 1 hou r after accidental death and the paraffin-embedded sections were ob-served by st reptavidin-peroxidase (SP) immunohistochemical methods.Result The expression of TSHR was observed in the perimysium, cytomembrane and cytoplasm in 10 of the 1 2 TAO specimens, accounting for a TSHR expression rate of 83.3% in the EOM of T AO patients. No TSHR protein was found in the healthy subjects.Conclusion High TSHR expression in the EOM of TAO patients indicates that as a common antigen b etween the orbit and thyroid, TSHR play a key role in the patho-genesis of TAO.