Two kinds of various morphological alpha-Fe2O3 nanoparticles modified by anionic surfactant (sodium dodecylsulfonate, SDS) and cationic surfactant (hexadecyipyridinium chloride, HPC), respectively, have been synthesized via hydrothermal method, using simple inorganic salt (NH4)(3)Fe(C2O4)(3) and alkali NaOH as starting precursors. Meanwhile, alpha-Fe2O3 nanoparticles without surfactant are also fabricated under the same conditions for comparison. The resultant products were characterized by means of Fourier transform infrared spectroscopy (FT-IR), Xray diffraction (XRD), transmission electron micrograph (TEM) combined with electron diffraction (ED) and magnetization measurements. It is interesting that the obtained alpha-Fe2O3 nanoparticles without surfactant are polyhedral with average particle size of 90 +/- 35 nm; while the obtained alpha-Fe2O3 nanoparticles modified by SDS are ellipsoidal with mean particle size of major axis: ca. 420 nm; minor axis: ca. 205 nm and those modified by HPC are spherical with mean particle size of ca. 185 nm observed from TEM. In addition, magnetic hysteresis measurements reveal that the alpha-Fe2O3 nanoparticles modified by two surfactants show enhancement in coercivity (H-c) and the remanent magnetization (M-r) compared with those of the obtained alpha-Fe2O3 nanoparticles without surfactant at room temperature. The experimental results suggest that the surfactants not only significantly influence the size and shape of the particles, but also their magnetic properties. (C) 2004 Elsevier Ltd. All rights reserved.