【Background】 Alternanthera philoxeroidesis a globally distributed invasive weed, causing serious economic and ecological damage in China. 【Method】 To investigate the toxic activity of A. philoxeroides, we prepared extracts by petroleum ether, chloroform, ethyl acetate and n-butyl alcohl. Repellency, contact and post-digestive toxicity of the extracts was tested on the lepidopteran pests Plutella xylostella and Spodoptera litura. 【Result】 (1) Each extract of A. philoxeroides had a repellent effect on both P. xylostella and S. litura. The effect of contact as well as postdigestive toxicity was stronger after longer extractin time; the corrected mortality rates and concentrations were positively correlated. (2) The corrected mortality of A. philoxeroides extracts by petroleum ether, ethyl acetate and n-butanol at a rate of 4000 g plant material/L of extraction agent on P. xylostella reached 70%, petroleum ether, ethyl acetate layer, nbutanol and water at a rate of of 4000 g plant material/L extracting agent and n-butanol and water layer of 500 g plant material/L extracting agent on S. litura reached 80%. 【Conclusion and significance】 The study had the reference value for the further research on A. philoxeroides and the development of new botanical pesticides.