ObjectiveTo observe the effects of hydroxysafflor yellow A (HSYA) on microvessel density (MVD) of mice transplanted Lewis lung cancer and mRNA expression of vascular endothelial growth factor (VEGF) so as to explore the tumor-inhibiting mechanism of HSYA. MethodsSixty tumor-bearing C57/BL mice were randomly divided into five groups, with 12 mice in each group, namely a control group, a cyclophosphamide (CTX) group (25mg/kg), a large dose HSYA group (112mg/L), a medium dose HSYA group (56mg/L), and a small dose HSYA group (28mg/L). These different drugs were administered by intraperitoneal injection. The mice were sacrificed 22 days after the treatment. Tumor tissues were sampled and examined by immunohistochemical method and quantitative real-time PCR to detect the expression of MVD and VEGF mRNA. ResultsThe MVD of the medium and small dose HSYA groups and CTX group were 30.01±3.12, 22.56±2.11 and 16.21±2.40, respectively, which were significantly lower than 41.10±2.93 of the control group and 37.66±3.04 of the large dose HSYA group (χ2=2.82, P=0.010;χ2=3.16, P=0.007;χ2=4.58, P=0.000) and (χ2=1.98, χ2=0.038;χ2=2.45, P=0.016;χ2=3.82, P=0.001). The difference in VEGF amplified fluorescence expression threshold between the HSYA groups and the control group was not significant. However, after amplification, the expression of VEGF mRNA in the small dose HSYA group was only 0.43±0.16, which was obviously lower than 0.82±0.06 in the control group (F=0.77, P=0.038). ConclusionHSYA can significantly reduce MVD in mice transplanted Lewis lung cancer and down-regulate expression of VEGF mRNA to achieve tumor-inhibiting effect.