An effective fraction from the fruiting bodies of Ganoderma lucidum, extraction method, use and preparation thereof are provided. The effective fraction is prepared from the defatted fruiting bodies of Ganoderma lucidum by extracting with alkali, dialyzing and drying. The effective fraction has effect of significantly lowering blood sugar.マンネンタケ子実体の効果的な分画、抽出方法、用途及び製剤である。前記効果的な分画は、マンネンタケ子実体の脱脂産物をアルカリ抽出、透析、乾燥して調製される。前記効果的な分画は、顕著な血糖降下効果を有する。