The present study proposes to use fluidized bed heat exchangers to improve thermal performances of high temperature heat exchangers for Stirling engines. Seven pot-type heat exchangers consisting of U-tubes with 6 mm outer diameter were inserted in a hot fluidized bed to measure heat transfer coefficients at the outer tube surfaces in the bed temperature range up to 400°C. Three different sizes of alumina particles were used as the bed material. The effects of particle size, tube number, fin size, superficial velocity, bed temperature, etc., were investigated. Also, the uniformity in temperature in the fluidized bed was found to be food enough to be used for heat exchangers of Stirling engines.