Ku Shen, Sophora flavescens Aiton (Leguminosae), contains alkaloids that possess broad biological activities. This study showed that total matrines (a mixture of the alkaloids), and matrine and oxymatrine (two major alkaloids) had a strong antifeedant effect against Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), at all tested concentrations (ranging from 0.01 to 5%). Total matrines and matrine also had significantly toxic effects at 5%. The estimated LD50 of total matrines and matrine was 12.3 and 8.6 microg per insect, respectively, after 24 h; 13.3 and 7.1 microg per insect after 48 h; and 10.1 and 4.8 microg per insect after 1 wk. The antifeedant and toxic properties of total matrines- and matrine-treated wood remained effective at least 12 mo after treatment under both light and dark storage conditions. These chemicals have great potential for commercial development as wood treatment agents.