To provide a gypsum-based investment material composition for casting and a method for manufacturing the same, the investment material composition being useful as a flash-heating-type gypsum-based investment material for making it possible to provide a product in which exposure time is reduced, such reduced exposure time not having been realized in the conventional product. A gypsum-based investment material composition for casting and a method for manufacturing the same, the investment material composition being a gypsum-based powdery investment material composition for casting, for use as a flash-heating-type investment material to which a malaxation liquid is added, the mixture is cured after malaxation, and the cured product is placed in a high-temperature furnace, wherein the gypsum-based investment material composition for casting has calcined gypsum, quartz, and cristobalite as main components thereof, the gypsum-based investment material composition for casting includes a powder or a liquid moisture-retaining component having a low water content and any one co-pulverized material selected from a co-pulverized material of calcined gypsum and quartz, a co-pulverized material of calcined gypsum and cristobalite, or a co-pulverized material of calcined gypsum, quartz, and cristobalite, and the gypsum-based investment material composition for casting has an average particle diameter of 30 [mu]m or less.本發明提供一種石膏系鑄造用包膜材組成物及其製造方法，其可提供習知製品所無法實現之縮短了放置時間之製品，可用作為急速加熱型石膏系包膜材有用。本發明係一種石膏系鑄造用包膜材組成物及其製造方法，其係加入練合液進行練合後使之硬化，將硬化體投入至高溫爐中之急速加熱型之包膜材用的石膏系粉體狀鑄造用包膜材組成物，其係以燒石膏、石英及白矽石作為主成分而成，且包含：自燒石膏與石英之共粉碎物、燒石膏與白矽石之共粉碎物或燒石膏與石英與白矽石之共粉碎物選擇之至少任一種共粉碎物；及粉體或含水率低之液狀保濕性成分；且該組成物之平均粒徑為30μm以下。
