The number of circulating endothelial progenitor cells (EPCs) was found to increase in patients with breast cancer, but the alteration in EPC function remains to be elusive. We conducted this study to evaluate the number and function of peripheral EPCs of breast cancer patients and its possible underlying mechanism. Besides, the vascular endothelial growth factor (VEGF), VCAM-1, IL-6, and IL-34 levels were measured in blood samples and also in vitro in a medium of EPCs. We found that the number of circulating EPCs in breast cancer patients was significantly higher than that in normal control and remarkably augmented in a stage-dependent manner. Meanwhile, a similar enhancement was observed in the migratory, proliferative, and adhesive activity of circulating EPCs originating from breast cancer patients. More importantly, the VEGF level in blood samples was dramatically elevated in comparison to the control, which was correlated positively with the number and activity of circulating EPCs from breast cancer patients. Moreover, in vitro medium of EPCs from breast cancer patients highly expressed VEGF compared with that from the control, which also had a positive correlation with the number and activity of circulating EPCs from breast cancer patients. This is the first time to demonstrate that the number and function of circulating EPCs are promoted in breast cancer patients, which are positively related to an enhanced VEGF production. These may provide a novel target for improving the outcome of breast cancer.