The objective of the research is to determine the effects of Fe(II) on the phase transformation from ferrihydrite to hematite in pH range 5-9 at 100degreesC. It is confirmed that Fe(II) is a catalyst in the process of phase transformation of ferrihydrite. On one hand, Fe(II) can catalyze the formation of hematite by a dissolution/reprecipitation mechanism. On the other hand, Fe(II) can catalyze the formation of hematite by a solid-state transformation. The species of Fe(II) that take catalytic action on the phase transformation of ferrihydrite are probably FeOH+ and Fe(OH)(2). Both dissolution/reprecipitation and solid-state transformation can be explained by electron transfer. This phase transformation from ferrihydrite to hernatite. which is called as catalytic phase transformation, can be employed to synthesize hematite particles rapidly. (C) 2004 Elsevier B.V. All rights reserved.