Experiments were performed in 1.5- and 150-1 reactors to investigate the growth process of needle-like goethite crystals under alkaline conditions. From an analysis of the transmission electron micrographs of the crystal samples during the reaction process, the nucleation and growth processes of the crystal grains were examined. Evidence shows that the nucleation of alpha-FeOOH crystals occurs both on the surface of the Fe(OH)(2) crystal grains and in the bulk liquid, depending on the local concentration of the alpha-FeOOH molecules. The statistical results of the particle size show that the average length and width are both basically proportional to R-1/3. The crystals grow in a similar manner and the size distribution is held roughly constant during the crystal growth process. The influence of the oxidation rate during the early period of the reaction process on the parameters of the final crystal grains was examined. The average aspect ratio of the final alpha-FeOOH grains increases with the decreasing of the oxidation rate in the early period. The particle size changes as a result of aging under certain pH and temperature conditions.