The preliminary results of insect antifeedant activity tests of crude hexane and dichloromethane extracts from the roots of Trigonostemon reidioides Craib. revealed that they displayed high activity. The separation of both crude extracts by column chromatography led to the isolation of 9 substances. By means of physical properties and spectroscopic data, they were characterized as a mixture of steroidal esters, a mixture of long chain acids, a mixture of steroids, acetyl aleuritolic acid, Trigonostemone, 5alpha-stigmastane-3,6-dione, 5-hydroxy-6,7-dimethoxy coumarin, a mixture of long chain amides, and a mixture of steroidal glycosides. From all separated substances, acetyl aleuritolic acids and a mixture of steroids are two active principles that showed highly active insect antifeedant activity. Furthermore, other two compounds were also isolated from ethyl acetate crude extract. Their structures were identified as 5-hydroxy-6,7-dimethoxy coumarin and 5,7-dihydroxy-6-methoxy coumarin. The latter was found to be a new naturally occurring coumarin.