Abstract: Objective: To investigate the influence of peripheral blood endothelial progenitor cells( EPCs) on the prognostic outcome of patients with acute ischemic stroke( IS). Methods: The peripheral blood EPCs( double-stained markers: CD133 / CD34) of 108 patients who had suffered from IS within 48 hours( stroke group),98 risk patients for cerebrovascular diseases( risk factor group) and 40 healthy volunteers( control group) were determined by flow cytometry. Meanwhile,the National Institutes of Health stroke scale( NIHSS) was used to evaluate the physical function and neurological impairment of the patients at the acute( 48 hours),convalescence( 21 days) and chronic phases of the stroke( 90 days). Results: The circulating EPCs level in the stroke group and the risk factor group was remarkably lower than that of the control( P 0. 01); patients with NIHSS12 had significantly lower level of EPCs than those with NIHSS 12( P 0. 01). High number of peripheral blood EPCs was closely associated with the improvement of NIHSS( 4) on day 21 after IS( P 0. 01) and independently associated with the good outcome on day 90 after IS( P 0. 01). Conclusions: The number of peripheral blood EPCs may act as an independently predictive maker for the prognosis of patients after IS.