The conventional polysaccharides having an immunostimulating activity have been used as medicinal agents, health foods and additives for livestock and fish feeds. However, most of the conventional polysaccharides do not exert a satisfactory immunostimulating activity. In these situations, the development of a composition which is inexpensive and exerts a high immunostimulating activity has been demanded. The present invention provides: a polysaccharide which is originated from an insect and has an immunostimulating activity； a composition containing the polysaccharide； and an immunostimulating agent containing the polysaccharide as an active ingredient. The polysaccharide according to the present invention preferably has at least rhamnose as a constituent sugar.迄今為止具有免疫賦活能的多醣作為醫藥品或健康食品、畜產用或水產用的飼料添加物進行利用，但是顯現出充分的免疫賦活效果之多醣相當少，因此尋求以低成本開發出顯現強免疫賦活效果之組合物；本發明提供源自昆蟲且具有免疫賦活作用的多醣類、含有該多醣類的組合物、以及以該多醣類作為活性成分的免疫賦活劑；本發明的多醣類之組成糖以至少含有鼠李糖為佳。
