ObjectiveTo explore the protective effect and mechanism of Qihong Tongluo prescription on vascular endothelial cells in rats with deep venous thrombosis （DVT）. MethodSixty-six SD rats were randomly divided into a blank group （n=11） and a modeling group （n=55）. The DVT model was induced in rats of the modeling group by slowing down blood flow and damaging vascular endothelium. The model rats were randomly divided into model group， aspirin group （200 mg·kg^-1）， and low-，medium-， and high-dose Qihong Tongluo prescription groups （6.5， 13， 26 g·kg^-1） according to a random number table. Rats were treated with corresponding drugs by gavage， while those in the model group and the blank group received normal saline， once per day for 7 days. The rats were sacrificed and the abdominal aortic blood was taken. The levels of serum endothelin-1 （ET-1） and interleukin-6 （IL-6） were detected by enzyme-linked immunosorbent assay （ELISA）. Hematoxylin-eosin （HE） staining was used to observe the pathological changes in vascular endothelial tissues. The ultrastructure of vascular endothelial cells was observed by the transmission electron microscope. The viability of vascular endothelial cells was detected by methylthiazolyldiphenyl-tetrazolium bromide （MTT） method，and the release level of lactate dehydrogenase （LDH） was detected by the LDH kit. The messenger ribonucleic acid （mRNA） expression of platelet-activating factor （PAF），nuclear transcription factor κB （NF-κB），Ras-related C3 botulinum toxin substrate 1 （Rac1）， and Ras-related C3 botulinum toxin substrate 2 （Rac2） in vascular endothelial tissues were detected by real-time reverse transcription polymerase chain reaction （Real-time PCR）. The protein expression of PAF，NF-κB，Rac1， and Rac2 in vascular endothelial tissues was detected by Western blot. ResultThe model group showed seriously damaged and swollen vascular endothelial cells with massive shedding， attachment of massive inflammatory cells， nucleus pyknosis and deformation under the electron microscope， highly swollen mitochondria， serious cytoplasmic vacuolation，and exposure of internal elastic membrane. The damage of vascular endothelium and its ultrastructure in Qihong Tongluo prescription groups and the aspirin group was improved in varying degrees. Compared with the blank group，the model group showed increased levels of serum ET-1 and IL-6，potentiated vascular endothelial cell viability， up-regulated mRNA and protein expression of PAF，NF-κB，Rac1， and Rac2 in vascular endothelial tissues，and decreased LDH release level of vascular endothelial cells （P<0.05）. Compared with the model group，the aspirin group and the Qihong Tongluo prescription groups showed decreased levels of serum ET-1 and IL-6，blunted vascular endothelial cell viability，down-regulated mRNA and protein expression of PAF，NF-κB，Rac1， and Rac2 in vascular endothelial tissues，and increased LDH release level of vascular endothelial cells （P<0.05）. The effect of Qihong Tongluo prescription was dose-dependent. ConclusionQihong Tongluo prescription has a protective effect on vascular endothelial cells of DVT rats and can prevent and treat thrombosis，and its therapeutic effect is presumably achieved by inhibiting the expression of PAF，NF-κB，Rac1，and Rac2 and reducing the levels of serum ET-1 and IL-6.