MIXING in a screen packed fluidized bed was studied using activated glass beads as a tracer. Glass beads of about 0.2mm were used as bed material. A 5cm Pyrex column was employed and longitudinal diffusivities were obtained. Diffusion model was successfully applied. Corelation given by Kang and Osberg was checked, which agreed well with the present experiment at lower air velocities. At higher air velocities a random walk model was proposed and gave good results.