Reaction　model　between　magnesia　and　graphite　in　resin　bonded　magnesia－carbon　bricks　is　proposed　based　on　the　measurement　results　of　weight　loss　values　and　texture　observation　of　two　types　of　resin　bonded　magnesia－carbon　bricks，named　sample　A　and　sample　B，after　heated　under　several　conditions　in　0．001atm． 　　Weight　loss　values　calculated　by　using　this　reaction　model　agree　with　experiment　values　comparatively　well．According　to　this　reaction　model，the　dominant　stage　of　the　reaction　in　the　early　stage　is　the　chemical　reaction　at　the　contacted　borders　between　magnesia　and　graphite，and　changes　to　be　the　diffusion　of　magnesium　vapour　and　carbon　mono－oxide　produced　by　the　reaction　as　time　goes　on．　Each　reaction　rate　coefficient　kr　of　chemical　reaction　between　magneisa　and　graphite　is　1．5×10-2％/min・cm2　in　the　sample　A　and　2．3×10-2％min・cm2　in　the　sample　B． Each　apparent　activation　energy　Ea　of　this　chemical　reaction　estimated　by　Arrhenius　plot　is　35kcal/mol　in　the　sample　A　and　76kcal/mol　in　the　sample　B．　lt　is　necessary　to　investigate　more　to　clarify　the　causes　of　the　difference　between　the　sample　A　and　the　sample　B．

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