Abstract： Objective To explore the relationship among 25-hydroxyvitamin D,serum calcium,calcium-sensing receptor,and breast cancer. Methods The expressions of calcium-sensing receptor (CaSR) in primary breast cancer,breast benign tumors,and normal breast tissue beside tumors were determined by immunohistochemistry S-P method as well as the concentration of serum 25 (OH) D and serum calcium in breast cancer and breast benign tumors by Enzyme-linked immunosorbent assay (ELISA),Tribromoarsenazo Ⅲ method.Results Serum 25 (OH) D level of breast cancer was significantly lower than the breast benign tumors [ (34.13 ± 14.14) nmol/L vs (50.29 ± 25.65 ) nmol/L,t =2.870,P =0.001 ].Serum level of 25 ( OH ) D in lymph node metastasis positive patient was lower than that in negative group [ (30.8 ± 9.71 ) nmol/L vs (43.7 ± 23.59) nmol/L,t =2.467,P =0.021 ].The positive expression of CaSR in breast cancer(88.9％ )was higher than breast benign tumors(60％,x2 =6.717,P ＜ 0.01 ) and normal breast tissue beside tumors (60％,x2 =5.628,P ＜ 0.05 ).Conclusions Concentration of serum 25 (OH)D and expression of calcium-sensing receptor in the tissues may be associated with occurrence,development and prognosis of breast cancer.