As a first stage of studies on the development of a fluidized bed incinerator for radioactive spent ion-exchange resins, the axial mixing characteristics of anion exchange resin beads and glass beads in a fluidized bed were investigated. The extent of axial solid mixing could be well characterized with a diffusion model and a global mixing index under various experimental conditions such as excess air velocities, size differences of particles and concentrations of resins. It was found that a certain extent of mixing of segregation was reached after 90 s. Axial diffusion coefficients are varing from 1 to 5㎠/s in this experimental ranges. The best conditions to incinerate anion resin beads with glass beads as bed materials in the gas-solid fluidized bed system, were 30wt% of resins in overall composition and excess air velocity over 8cm/s with glass beads having an averaged diameter of 320㎛.