Hematite nanocrystals modified with surface layers of amorphous hydrous iron oxides were prepared by hydrothermal conditions in the absence of alkali. The formation temperature was found to be ca. 130degreesC. When the temperature was lower than 130degreesC, no product was formed, while above this temperature, the amount of amorphous hydrous iron oxides at the surface of hematite nanocrystals was drastically decreased. The amorphous layers on the hematite nanocrystals obtained at 130degreesC were determined to be Fe2O3.1.64H(2)O. The coercivity for the hematite nanocrystals with modified layers was 0.534 kOe, which is slightly larger than the values for hematite nanocrystals with few agglomerations. (C) 2002 Elsevier Science Ltd. All rights reserved.