PURPOSE: To highly simply prepare an Allium plant composition containing S-allyl-cysteine in a high concentration by adding cysteine to a process for processing the allium plant.

CONSTITUTION: An Allium plant (e.g. garlic, elephant garlic, Welch onion, leek, scallion), preferably a bulk thereof, in a raw state or in a dried or frozen and pulverized state is extracted with water or a lower alcohol (preferably ethanol) at a pH of 8-10 and a temperature of 30-50°C and mixed with cysteine in an amount of 0.1-20wt.%, preferably 1-5wt.%, based on the wt. of the plant at an arbitrary time in the process preferably just after the extraction to provide a composition containing S-allyl-cysteine having hepatic function-suppressing activity, radiation-protecting activity, tumor generation-suppressing activity, etc., in a high concentration. The composition is useful as a raw material for drugs, cosmetics or foods.