Abstract: Fluidized bed mixer offers the most efficient and economical process compared to other mixers. However, less effort has been devoted to understand the local behavior of the solids in fluidized bed, partly due to the lack of reliable experimental methods. Thus, the objective of this paper was to view the local mixing behavior and property of a free flow polymer binary mixture in bubbling fluidized bed. In this work, an experimental study of mixing process of free flowing polymers binary mixtures at different densities and colors in bubbling fluidized were investigated. The mixing properties were studied by analyzing the variation of the proportions of the marked particles with time and position in the bed. The variation of mixture composition based on the samples incorporated into Lacey mixing index that describes the degree of mixing of the particle at particular time. This method enables the assessment of the overall mixing behavior in terms of the rate of mixing (through...