In the search for biologically active substances from Thai medicinal plants Crude extracts from the roots of Trigonostemon reidioides Craib (Euphorbiaceae) have shown a strong inhibition of insect (Boll weevil) feeding. Fractionation of curde hexane via column chromatography led to the isolation of a mixture of β -sitosteryl palmitate, stigmasteryl palmitate, campesteryl palmitate and chloresteryl palmitate, a mixture of long chain acid (C₁₆-C₃₅), a mixture of β-sitosterol, stigmasterol and campesterol, acetyl aleuritolic acid and 5∝-stigmastane-3,6-dione. Moreover, a novel compound,1,1,7-trimethyl-3,6-9-trimethoxy phenanthrenone, named Trigonostemone was isolated. The other three compounds obtained from crude dichloromethane and chloroform, 5-hydroxy-6, 7-dimethoxy coumarin, a mixture of long chain amides (C₄₄-C₄₈) and a mixture of β-sitosteryl-3-0-glucopyranoside, stigmasteryl-3-0-glucopyranoside and campesteryl-3-0-glucopyranoside. The structure of these compounds were established on the basis of physical properties, chemical properties and spectral evidences. The determination of the water soluble fraction constituents of both parts as chloride salts, sugars and amino acids was also reported.