The use of Fe Fischer-Tropsch (F-T) catalysts in slurry bubble column reactors (SBCRs) has been problematic in the past because of their poor attrition resistance. Recently, we have reported the preparation of spray-dried Fe F-T catalysts having attrition resistance suitable for SBCR use, but the reason for this improvement was not clear. This paper focuses on research done to better understand:the reason for the high attrition resistance of some of the Fe catalysts prepared. Understanding the relationship between the catalyst attrition resistance and composition/structure is important for the preparation of attrition-resistant Fe catalysts. In the present study, two series of spray-dried Fe F-T catalysts having the composition Fe/Cu/K/SiO2 but with different amounts of precipitated and/or binder SiO2 were investigated. All of the catalysts studied were evaluated in their calcined form. This was done to minimize any possible attrition due to Fe phase change (such as can occur during activation and F-T synthesis) in order to address the effect of the other catalyst properties. A companion paper addresses-attrition due to phase change after carburization. It was found that:particle density, principally among other particle properties of the catalysts, correlated with the intrinsic catalyst attrition resistance. Changes in fluidization in the jet cup-attrition test with changes in particle density only had minimal effects on the results. Particle density differences reflected differences in the catalyst inner structure. Differences in SiO2 type and concentration resulted in different structures for the SiO2 network and therefore affected the catalyst structure.