Abstract: Objective To study antitumor effect of β-sitosterol and its mechanism in H₂₂ tumor-bearing mice.Methods The tumor-bearing ICR mouse model was established with intraperitoneal injection of H₂₂ cell suspension and the 10 mice with intraperitoneal injection of normal saline were used as the controls.Then the model mice were randomly divided into a model group,a cyclophosphamide (30 mg/kg) group,and low-and high-dose β-sitosterol (10 and 50 mg/kg) groups (10 mice in each group).All the treatments were administered through intraperitoneal injection once a day continuously for 14 days.At the end of the treatments,the weight of tumor tissues from the tumor-bearing mice was determined and the tumor inhibition rate,the spleen index and the thymus index of the mice were calculated;in addition,serological parameters were measured and the histopathological changes in organs of the mice were observed.Results Compared with that of the model group,the weight of tumor tissues was significantly lower in the mice of cyclophosphamide and low-and high-dose β-sitosterol group (P<0.05 for all);the tumor inhibition rates were 56.1% in the mice of cyclophosphamide group and 53.0% and 41.4% in the mice of low-and high-dose β-sitosterol group.The serum levels of interleukin-6 (IL-6,1112.47±76.15 pg/mL) and vascular endothelial growth factor (VEGF,512.75±22.55 pg/mL) of the model group were significantly increased compared with those of the controls (both P<0.05).Compared with that of the model group,the serum levels of IL-6 (341.31±31.19 pg/mL) and VEGF (356.92±19.45 pg/mL) of the high-dose of β-sitosterol group were significantly decreased,while the level of interferon-γ (IFN-γ,122.92±13.66 pg/mL) was significantly increased (P<0.05).Necrosis of tumor tissues and obviously more apoptosis of tumor cells compared to that of the model group were observed in the mice of the β-sitosterol groups.Conclusion β-sitosterol exhibits a certain antitumor effect in H₂₂ tumor-bearing mice and the mechanism may be related to the regulation of IL-6,IFN-γ and VEGF expression by β-sitosterol.