Surface chemical states of 57Co2+ and 119Sb5+ ions adsorbed on γ-Fe2O3 and NiFe2O4 were studied in the presence of the aqueous phase using the magnetic interaction between the substrates and 57Fe2+ or 119Sn4+ arising from the adsorbed species. Two chemical forms were observed for the 57Co2+ adsorbed on γ-Fe2O3; one giving a peak in the high-field region and another giving a broad distribution in the lower fields, which were attributed to 57Co2+ at surface B sites of the spinel structure of γ-Fe2O3 and 57Co2+ species weakly bonded to the substrate, respectively. In case of the NiFe2O4 substrate, the latter species was dominant and was converted to the former by heating. Most of the 119Sb5+ ions adsorbed on the γ-Fe2O3 and NiFe2O4 particles were found to have a certain magnetic interaction with the magnetically ordered ions of the substrates.