Nanosized gamma-Fe2O3 is synthesized by the microwave-hydrothermal method. Powder X-ray diffraction and transmission electron microscopic studies showed that the average particle size is 10 nm. Magnetic studies reveal that the gamma-Fe2O3 nanoparticles are superparamagnetic at room temperature, with a superparamagnetic blocking temperature of 200 K. The magnetic characteristics of the nanoparticles indicate their strongly interacting nature. (C) 2006 Elsevier Ltd. All rights reserved.