Catalyst attrition has often been a major obstacle in the development of new fluidized-bed-processes and it is still of concern for existing processes whenever the catalyst is changed. The main consequence of attrition is the generation of fines and the resulting loss of valuable material. In this work the attrition of FCC catalysts in a fluidized-bed system consisting of a bubbling bed, cyclone gas cleaning, and external solids recirculation is studied. An approach developed describes the attrition-induced overall solids loss based on the main attrition sources grid jet attrition, bubble-induced attrition and attrition in the cyclone. Their respective contributions to the overall attrition rate are calculated from separately derived model equations that take into account the design of the system, the operating conditions, and the material properties of the catalysts. The solids entrainment from the bed into the cyclone is shown to have a strong effect on the attrition-induced loss rate and must therefore be taken into account for an a-priori prediction.