Abstract： Objective To observe the effect of butylphthalide on the endothelial progenitor cells of peripheral blood and the score of NIH stroke scale in the acute ischemic stroke patients,and explore the efficacy and mechanism of NBP treatment on ischemic stroke.Methods 96 cases with first acute ischemic stroke within 48 hours of onset were admitted in our hospital and randomly divided into NBP group and placebo group.30 days was a course of NBP treatment.EPCs were marked as CD34 +/CDI33 +/KDR + labeled ceils by flow cytometry detection.EPCs levels were detected at baseline,7 days,14 days and 30 days after therapy in all the patients.NIHSS scores were also detected at the same time and 90 daysafter onset.Results The levels of EPCs of NBP group was significantly increased at 7 days,14 days and 30 days after therapy when compared with those of baseline ( P ＜ 0.05,respectively) and they were also markedly higher than those of placebo group in the same period (P ＜ 0.05,P ＜ 0.001,P ＜ 0.001 ).NIHSS score was not obviously changed after 7days NBP treatment (P ＞ 0.05 ),but it was continuously decrease at 14 days,30 days and 90 days.Also it was significantly lower than that of placebo group at 14 days and 30 days in NBP group ( P ＜ 0.05,respectively).During the follow - up period ( within three months after onset) ischemic events in NBP group were slightly lower than those of placebo group ( P ＞ 0.05 ).There were no serious adverse effects in the two groups.Conclusions NBP treatment could obviously improve neurological score in the acute ischemic stroke patients and it is possibly by increase the levels of circulating EPCs to improve the prognosis.It is well tolerated.