Temporal stability of magnetic parameters of anthropogenic ferrimagnetics in model soil conditions was studied. Fly ash from a power plant was used as original contaminant m aterial, while soil reactive medium was modeled by different soil solutions. Changes in massspecific magnetic susceptibility ( ), percentage frequency dependent magnetic susceptibility ( F D %), hysteresis parameters and thermomagnetic curves were measured for samples which underwent different leaching time periods. Virtually constant magnetic susceptibility values were obtained, independently on the soil medium (acid, neutral). On the other hand, the original highly non-stoichiometric maghemite phase rapidly transformed to stable magnetite. In some cases (model of free-draining soils) further decrease of Curie temperature (T c ) to 550-560 o C is observed.