Objective To explore the possible mechanism of Xuefu Zhuyu Capsule（XZC

血府逐瘀胶囊） in regulating angiogenesis. Methods XZC-containing serum and blank serum were prepared. Human microvascular endothelial cells（HMEC-1） were given 1.25%

2.5% and 5% of XZC-containning serum or blank serum for 24 h

48 h and 72 h each group was provided with 3 multiple wells. In vitro assays of angiogenesis was performed for assessment of cell lumen formation. The optimal concentration of XZC-containing serum which promoted lumen formulation first and inhibited it later was used for further tests; XZC-containing serum or blank serum of optimal concentration were given to HMEC-1 for 12 h

24 h or 48 h; real-time quantitative PCR and Wesstern Blotting were used to detect Krüppel-like factor 2（KLF2） protein and mRNA levels. Results The number of lumen of HMEC-1 cells significantly increased after administration with 1.25% or 2.5% XZC-containing serums for 48 hours（P<0.05 or P<0.01）; after 72 h intervention with XZC-containing serum

the number of lumen significantly increased when the concentration was 1.25% while decreased when it was 2.5%（P<0.01）. Compared to XZC-containing serum of the same concentration administered for 24 h

1.25% XZC-containing serum administered for 48 h and 72 h

as well as 2.5% XZC-containing serum for 48 h significantly increased the number of lumen（P<0.01）; compared to XZC-containing serum of the same concentration administered for 48 h

2.5% XZC-containing serum for 72 h significantly reduced the number of lumen（P<0.01）. Therefore

2.5% XZC-containing serum was selected for further tests. Compared to those of the blank serum group

the 12 h and 24 h KLF2 protein and mRNA levels of the XZC-containing serum group were not significantly different（P>0.05）; the 48 h KLF2 protein level significantly decreased while 48 h KLF2 mRNA level increased（P<0.05 or P<0.01）. Compared to those of the XZC-containing serum group administered for 12 h and 24 h

the 48 h KLF2 protein expression was not statistically different（P>0.05）

and the 48 h KLF2 mRNA level significantly increased（P<0.05）. Conclusion The mechanism of XZC in regulating angiogenesis may be related to the decrease of KLF2 protein level and mRNA level.