Objective:To study the anti-tumor effect of neo-gambogic acid(NGA)on Hep G2 xenograft in nude mice in vivo and its mechanism. Method:Sixty healthy BALB/c-nu mice

transplanted by Hep G2 hepatocarcinoma cells

were divided into 5 groups

including model group

5-FU(10.0 mg·kg-1) group and three groups of neo-gambogic acid in high dose

middle dose and low dose(8.0

4.0

2.0 mg·kg-1). The mice were executed after fourteen days of treatment every other day (qod) and tumor tissues were excised. The size of tumor tissues was measured and tumor inhibition rate was calculated. Immunohistochemistry was used to detect the expressions of Bax

Bcl-2

p-ERK1/2 and p-MEK1/2. Result:the tumor weight of NGA groups was reduced remarkably compared with control group. The tumor inhibition rate of NGA high-dose (8.0 mg·kg-1) group was 83.75%

which excelled the tumor inhibition rate of the 5-FU (10.0 mg·kg-1) group (46.54%

P＜0.05). The expression of Bax was up-regulated by NGA dose dependently while the expression of Bcl-2 was down-regulated. The expressions of p-ERKl/2 and p-MEKl/2 in NGA groups were reduced remarkably compared with control group (P＜0.05). Conclusion:NGA exerts exact anti-tumor effect on Hep G2 xenograft in nude mice in vivo. Its mechanism correlates with that the cells in Hep G2 xenograft are induced apoptosis via up-regulating the Bax/Bcl-2 ratio and that the phosphorylation level of mitogen-activated protein kinase (MAPK) signal transduction pathway is down-regulated.