Waste incineration fly ash (Fa), pretreated by washing with distilled water and heating at 1000 degrees C in air, was treated with various concentrations of octyl phosphate [C8H17OPO3H2(OP)] aqueous solution by stirring at 25 degrees C for 3 h and aging at 85 degrees C for 24 h. X-ray fluorescence and X-ray diffraction measurements indicated that the major element of Fa is Ca which exists as CaO and gehlenite (2CaO center dot Al2O3 center dot SiO2). Treating Fa in OP solutions dissolved the CaO and gehlenite to form calcium octyl phosphate (C8H17OPO3Ca center dot nH(2)O), which is composed of a multilayer alternating dicalcium phosphate dihydrate (CaHPO4 center dot 2H(2)O)-like phase and a bimolecular layer of octyl groups of the phosphates. Increasing the OP concentration increased the fixed amount of OP and amount of recovery after the treatment. The fixed amount and amount of recovery steeply increased during stirring at 25 degrees C, and were almost unchanged by aging. These facts allow us to infer that Fa is available to fix alkyl phosphate ions such as OP.