A large decrease in fluidization quality was observed in the reactions involving the decrease in gas volume due to reactions. The upper part of the emulsion phase was defluidized and this part was lifted up through the column like a moving piston. The cause was the decrease in the gas velocity in the emulsion phase. The calculation showed that the gas drag force became small not enough to balance with gravitational force and buoyancy force acting on particles in the emulsion phase even when the gas flow from bubble to the emulsion phase was considered. In the present study, internals Were used to prevent the defluidization and to improve the fluidization quality. The effects or the position and number of plates were Studied. The horizontal metal sieves enhanced the fluidization quality. It was difficult to destroy the defluidized part moving through the column by the metal sieves installed in the tipper part of the bed. However, the metal sieves successfully prevented the generation of the defluidized part when they were installed in the lower part of the bed.