Objective:To investigate the serum 25-hydroxyvitamin D [25(OH)D] level in patients with Graves' disease (GD) and its correlation with thyrotropin receptor antibody (TRAb) and bone metabolism markers.Methods:A total of 124 patients with newly diagnosed or relapsed GD were selected and divided into three groups according to serum 25(OH)D level, namely vitamin D deficiency group with 25(OH)D <12 μg/L, vitamin D insufficiency group with 25(OH)D of 12 to 20 μg/L, and vitamin D sufficiency group with 25(OH)D ≥ 20 μg/L. The levels of serum 25(OH)D, TRAb, type I procollagen N-terminal pro-peptide (PINP), type I collagen cross-linked C-terminal peptide (S-CTX), parathyroid hormone (PTH), total triiodothyronine (TT 3), total thyroxine (TT 4) and thyroid-stimulating hormone (TSH) were measured in all patients, and the differences of these biochemical indices were compared across groups. Oneway analysis of variance or Kruskal-Wallis test was used for comparison between groups, and Pearson or Spearman correlation analysis was applied for correlation test. Results:The levels of serum TT 3, TT 4, PINP, and S-CTX significantly increased ( P < 0.01) and the level of phosphorus (P) decreased ( P < 0.01) with the decreased vitamin D levels. The levels of PTH and calcium (Ca) were significantly lower in the vitamin D sufficiency group compared with the vitamin D insufficiency group and vitamin D deficiency group ( P < 0.01). Correlation analysis showed that serum 25(OH)D level was negatively correlated with the levels of TT 3, TT 4, PINP, S-CTX, PTH and Ca ( P < 0.01), and positively correlated with the levels of P and TSH ( P < 0.01). Conclusions:Decreased serum 25(OH)D level is closely related with increased bone turnover, PTH, and thyroid hormone levels in patients with GD, but not related with TRAb. Thyroid hormone levels have a certain predictive value regarding vitamin D deficiency in GD patients. It is necessary to monitor the vitamin D levels in patients with GD and provide vitamin D supplementation to reduce the incidence of osteoporosis, improve the effectiveness of antithyroid treatment and reduce the recurrence of GD.