Abstract: Objective: To investigate the value of interleukin-11(IL- 11) and connective tissue growth factor (CTGF) in the diagnosis of bone metastasis of human breast cancer and to explore new markers for early diagnosis of bone metasta -sis of human breast cancer. Methods:The serum levels of IL-11and CTGF in 180 cases of breast cancer, 45cases of bone metastasis of other types of cancer, and that of20healthy controls were determined by ELISA assay. Results: IL-11level was significantly higher in breast cancer patients with bone metastasis than in healthy controls and patients with no bone metastasis (P<0.05). CTGF showed no statistical significance ( P>0.05) among these groups. Compared to the healthy con-trol group, CTGF level was higher in the breast cancer bone metastasis group (P<0.05), but showed no significant differ-ence in the breast cancer with no bone metastasis group ( P>0.05). IL-11level was higher in the breast cancer patients with bone metastasis (P<0.05) and showed no significant difference in the breast cancer patients with no bone metastasis (P>0.05), when compared with healthy controls. In patients with bone metastasis of breast cancer, IL- 11level was correlated with patient age, the degree of bone pain and level of bone metastasis ( P<0.05). Conclusion:The quantitative determina-tion of IL-11is helpful for the diagnosis of bone metastasis of breast cancer and could be used as a new serum marker.