Objective To observe the influence of Tongxinluo Superfine （Submicron powder of Chinese medicines for preventing the atherosclerosis） on the endothelial cells and its mechanism. Methods Healthy male Wistar rats were randomized into normal group and model group. The model group was given a methionine diet plus basic diet and weight-loading swimming to establish the models of endothelial dysfunction in the collateral qi deficiency and stagnation syndrome. The serum of mice of the normal group and model group was used to culture in vitro the cell line of human umbilical vein endothelial cells （HUVEC） in an experiment of four groups

i.e. blank group

normal serum group

model serum group

and Tongxinluo Superfine group. The changes in the morphological structure and distribution and content of fibrous actin （F-actin） of endothelial cytoskeletal protein 6 hours after the serum functioned on HUVEC were observed. Results In the model group

a significant destruction of F-actin appeared after the serum functioning for 6 hours

and decreased fluorescence intensity existed. The preprocessing of HUVEC with Tongxinluo Superfine could reduce the incidence of damage of F-actin and increase its content （P<0.01）. Conclusion Tongxinluo Superfine can weaken the damage of F-actin of endothelial cytoskeletal protein

being part of the possible mechanism in improving the endothelial functions of vessels to prevent the atherosclerosis.