Abstract: Objective：To investigate the antitumor effect of Huaier aqueous extract on xenografted lung cancer in nude mice. Methods：Xenograft model of lung cancer was constructed in nude mice, and the mice were treated with Huaier aqueous extract. Nude mice were randomly divided into experimental group and control group, and were treated with 0.2 mL Huaier aqueous extract (with the dose of 1 g/kg, 3 g/kg, 5 g/kg, and 7 g/kg, respectively) or 0.9% saline intragastrically once every 3 days for 3 weeks. The tumor volume and the changes of body weight of nude mice were observed, and the tumor weight was compared. The pathological changes of tumors and the ratio of Ki-67 positive cells were observed under microscopy. Results：After inoculation of lung cancer cells in nude mice for 14 days, tumor growth occurred in all inoculated sites.. The tumor growth inhibition rates in the 1 g/kg, 3 g/kg, 5 g/kg, and 7 g/kg groups were (1.73±12.99)%, (6.68±11.34)%, (46.24±9.17)%, and (35.05±12.15)%, respectively. Compared with the control group, the tumor growth inhibition rate was significantly increased in the groups of 5 g/kg (P=0.0044) and 7 g/kg (P=0.0215). The tumor weight in the 5 g/kg group was lower than that in the control group, but there was no statistical difference. Ki-67 immunohistochemistry staining showed that the proliferation rate of tumor cells in the groups of 3 g/kg, 5 g/kg, and 7 g/kg was significantly lower than that in the control group, and Ki-67 positive rate in 7 g/kg group was the lowest (24.8%, P<0.001). Conclusions：In nude mice, Huaier aqueous extract can inhibit the proliferation activity of lung cancer cells, thereby inhibiting tumor growth.