Attrition experiments with granular slugs were performed in a fluidized bed. A single horizontal nozzle was equipped on the sidewall of the fluidized bed in order to distinguish the effect of jet gas flow on attrition from the auxiliary fluidizing gas supplied from the distributor. The analysis was mainly focussed on the change in the granular slug weight. Reduction of particle size was mainly due to the attrition of its surface or irregularities, and breakage into two or more small particles was not observed. A new attrition model, where the generation rate of fines is assumed to be in proportion to the weight of particle, and the effect of fluidizing gas supplied from the distributor on the attrition was assumed to be neglected, is proposed. The measured attrition data were correlated well by this model, and its reliability was examined. The coefficient K included in the proposed model, which is concerned with energy transfer to attrition, is almost independent of the initial weight of particles, and increases with jet flow rate.