beta-FeOOH particles were synthesized in the presence of Ti(IV), Al(III), and Cr(III) at metal/Fe atomic ratios of 0-0.1 by the following two methods: hydrolysis of aqueous FeCl3 solutions added to the hydrolysis products of these metal ions (subsequent hydrolysis, SH) and hydrolysis of aqueous FeCl3 solutions dissolving these metal ions (combined hydrolysis, CH). On increasing Al/Fe the particle size of the products with AlCl3 by SH method steeply rose at a low Al/Fe and then fell. The similar increase of particle size was seen in SH method with Ti(SO4)(2) though the addition of TiCl4 decreased the particle size. In CH method, Ti(IV) markedly impeded the beta-FeOOH formation but Al(III) and Cr(III) showed no influence. The particles prepared by CH and SH methods contained a large amount of Ti(IV) but a few AI(III) and Cr(III). The large spindle-shaped and rod-shaped particles produced by SH method with AlCl3 and Ti(SO4)(2) were highly microporous and poorly crystallized, indicating that the particles consist of fine primary particles and the aggregation of fine particles would be promoted by SO42-. The different influences of the metal ions on the beta-FeOOH formation were explained by their hydrolysis characteristics. (C) 2003 Elsevier Inc. All rights reserved.