We describe the evolution of catalyst microstructure as a precipitated Fe-Cu catalyst precursor is transformed into an attrition resistant Fischer-Tropsch (F-T) catalyst. The precipitated Fe-Cu catalyst, as-prepared, is weak compared to the same catalyst that was spray-dried, but without a binder. Spray-drying improves the attrition resistance of the catalyst. Ultrasonic fragmentation was used in this work to measure the attrition resistance of the slurry phase catalysts. Both catalysts, after ultrasonication, produce fine particles below 5 mu m, which could cause filtration problems in slurry F-T reactors. The addition of silica as the binder improved the catalyst＇s attrition resistance with negligible generation of fine particles below 5 mu m. Cross-section TEM of the SiO2-containing Fe F-T catalyst shows that the crystallized Fe particles with an average particle diameter of 80 nm are uniformly distributed within a silica binder. This study provides insight into the catalyst microstructure that leads to improved attrition resistance in Fe F-T catalysts. (C) 2000 Elsevier Science B.V. All rights reserved.