Objective To study the relationship between red blood cell distribution width (RDW) and thyroid associated ophthalmopathy (TAO). Methods Fifty-two patients with Graves'disease (GD, 18 males and 34 females,39 cases of GD patients with Graves' ophthalmopathy [GO])and 22 healthy controls (8 males and 14 females) were recruited in the present study. The RDW and thyroid functions were measured in all participants. Ophthalmological examinations including Hertel's exophthalmometer readings (HER) and clinical activity score (CAS) evaluation were obtained in GD patients, and the results were compared between different groups. Results Thyroid functions were significantly different between GD patients and healthy controls (P<0.05), while they were not between GD patients with or without GO; the HER level was significantly higher in those with GO compared with those without GO(P<0.05). The RDW value in patients with GD was significantly higher than that in the healthy controls (P<0.05). For GD patients, RDW increased with the increase of CAS, and those with GO had significantly higher RDW than those without GO(P<0.05). Conclusion RDW is associated with the state of the GD patients, indicating that RDW may provide evidence for assessing the severity of GO.