A conceptual fluidized bed blanket and its cooling method is proposed in which particles of breeding materials are fluidized by a coolant gas. To further this concept, fundamental experiments were carried out in order to enhance the efficiency of heat transfer between fluidized particles of the breeding material and the coolant gas. Experiments using pre-heated glass beads and air were made. Heat transfer was enhanced by the well mixed particles and the uniformly distributed temperature in a simulated fluidizing bed. A new model for determining the mean heat transfer coefficients between fluidized particles and gas in various type of gas-solid fluidized beds is discussed.