In this study, an ethanol extract being obtained from Allium cepa var. cepa examins the inhibitory effects on the glutathione S-transferase and the separation had been done by silica-gel column chromatography using various eluents, such as ethyl acetate, methanol, and 50% methanol. A volume of column fraction was 50ml and evaporation has been performde by the rotary evaporator under reduced pressure. Each fraction is being examined by thin layer chromatography and the UV spectrum at 365 nm was used to investigate separation patterns of spots on thin layer chromatography. When the eluent was changed, the spot patterns showed another different pattern on thin layer chromatography, so on. Fractions showing similar pattern are combined and eventually, three fractions are obtained. Each fraction is testified to examine the inhibition effects on glutathione S-transferase. All of these showed inhibition effects on glutathione S-transferase. The GC-MS shows that each fraction contains more than 2 compounds.