Severe defluidization occurs when reactions accompanied by a decrease in mole number are performed in a gas-solid fluidized bed. This phenomenon is due to a decrease in gas velocity to below the minimum fluidization velocity in the emulsion phase. For the stable operation of a fluidized bed reactor, it is important to control the gas volume reduction rate by reducing the reaction rate. However, this method leads to a low conversion at the reactor outlet. In order to increase the overall conversion, therefore, unreacted components should be separated from the product gas and recycled to the reactor inlet. We studied the gas recycle method on the basis of experimental data reported in previous studies and a fluidized-bed reactor model by considering the decrease in mole number. Because defluidization tends to occur when the gas volume reduction rate increases with the reaction rate, defluidization is minimized when the reaction rate constant reaches its maximum value. In this study, we established the influence of reaction conditions on the maximum reaction rate constant and the minimum recycle ratio.