In this work,mixing and segregation of binary mixtures involving biomass materials in a fluidized bed was experimentally investigated.A frozen bed method was employed to investigate both axial and radial distribution of biomass particles in silica sand.Three different biomass materials were studied:willow sawdust,pelletized soy and oat hull materials.Biomass loading investigated ranged from 5％to 30％by weight.The extent of mixing for each of the biomass composition was investigated using Lacey\'s mixing index which is based on the standard deviations of the sample at different axial positions in the bed.The radial composition was also investigated by means of digital imaging analysis using a high-resolution digital camera.The experiments revealed the differences in the extent of particle distribution for pelletized biomass materials vs non-densified materials as a result of differences in particle size,density and importantly,the particle shape of the materials utilized.The results showed an increase in the extent of mixing as the fluidizing velocity increased for both pellet materials while the mixing index for sawdust decreased beyond a loading of 20％.With an increase in biomass loading,an increase in mixing index was found for the two pellet materials.A similar trend was observed for sawdust at the lower loading level.However,the mixing index started to decrease at higher loading level beyond 20％.The results greatly contributed to the understanding of the hydrodynamics of binary and multicomponent mixtures involving biomass materials,especially pelletized materials in fluidized beds.