The fluidization behaviors of binary mixtures of biomass and quartz sand were investigated in an acoustic bubbling fluidized bed. Two kinds of biomass particles, sawdust and wheat stalk, were employed in this test. The experiments indicated that the addition of quartz sand can improve the fluidization quality of biomass. The minimum fluidization velocity of the mixtures increased with increasing biomass content in the mixtures. A new correlation was developed for predicting the minimum fluidization velocity of different binary mixtures. The minimum fluidization velocity decreased with increasing sound pressure level and had a minimum value over the sound frequency range of 100-200 Hz. Such an acoustic fluidized bed operated in a stable or unstable fluidization regime depending oil the operating conditions. According to the slope of a plot of standard deviations, unstable fluidization call be expected if the slope is greater than 50, and stable fluidization can be expected if the value is less than or equal to 50.