Gas-solid fluidized beds are applied in biomass gasification technology and therefore a number of types of gasifiers had been developed to meet the need. Compartmented Fluidized Bed Gasifier (CFBG) is one of them, and is considered more efficient than others as the design is compact and low cost. The allocation of heat and mass between two compartments, combustor and gasifier of CFBG are mainly attained by means of solid circulation. Therefore, the main purpose of this research is to study the effect of main bed aeration.