The solvation effects on :the electronic structures and magnetic properties were computed for a series of ferrocenium cations in the ferrocenium-based ionic liquids using RISM-SCF-SEDD calculations coupled With CASSCF. The spin orbit coupling was calculated tu get insight into the spin anisotropy. The values were on the order of 100 cm(-1), exhibiting strong spin anisotropy parallel to the angular momentum. The computed results show that the magnetic properties of ferrocenium cations are similar both in the isolated state and in ionic liquids. We also carried out molecular dynamics and RISM calculations to investigate the liquid structures. The radial and spatial distribution functions around the cations indicate that the cations are surrounded by about seven TFSA anions above and below the cyclopentadienyl rings and from the side of the ferrocenium cations. The nearest-neighbor cations exist in the oblique directions. The introduction of a butyl group to the ring disturbs the solvation structures, and butyl groups in different cations tend to attract each other like those observed in alkylimidazolium ionic liquids.