It　has　been　a　mutual　recognition　among　the　researchers　concerned　that　the data　of　internal　steam　pressure　in　the　process　of　drying　are　prerequisite　to　solve the problem　of　explosive　spalling　of　monolithic　refractories．　However，such　studies　have　been　rarely　conducted． 　　This　paper　describes　about　the　development　of　a　measuring　apparatus　for　internal　steam　pressure　within　castables　during　drying　and　the　results　of　measured　internal　steam　pressures　with　a　clay　bonded　castable　and　a　dense　low　cement　castable． 　　　It　has　clearly　shown　that　the　internal　steam　pressure　with　these　castables　increases　with　the　decrease　of　curing　temperature，ana　the　necessary　drying　temperature　is　fairly　higher　than　the　conventionally　settled　level，i．e．more　than　150℃　for　the　clay　bonded　castable　and　ca．200℃　for　the　dense　low　cement　castable．Moreover，a　computer　simulation　study　of　drying　has　been　conducted．　From　both　studies　of　experiment　and　slmulation，it　has　been　assumed　that　the　drying　of　castable　refractory　structure　proceeds　not　only　with　vaporization　of　water，but　also　intimately　related　with　water　migration　in　liquid　state　within　capillary　pores　of　castables．The　increase　of　intemal　steam　pressure　with　the　decrease　of　curing　temperature　is　ascribed　to　the　retaining　of　combined　water　which　cannot　join　to　the　capillary　movement　of　water　in　the　process　of　migration　drying　inliquid　state．

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