In this paper, the microspherical Fe2O3 was successfully obtained by calcining the FeCO3 sphere prepared by a hydrothermal route. The sphere morphology perfectly remained after the calcination of FeCO3 but the diameter of sphere decreased in a certain degree from 70-100 mu m to 50-70 mu m, which might be due to some loss of quantity during the calcination (FeCO3-Fe2O3). The sphere was solid and highly densified. At the same time, the effects of factors influencing the formation of FeCO3, such as PVP, reaction temperature were investigated. The simple formation process of FeCO3 was also proposed as follows: Fe2+ produced by the reduction of Fe3+ reacted with CO32- released from the decomposition of urea to form FeCO3 nanoparticle. Then, the formed nanoparticles aggregated together to produce sphere structure via oriented attachment. With the reaction time increasing, the sphere became solidness and densification. (C) 2010 Elsevier Inc. All rights reserved.