Fine particles of barium hexaferrite were prepared from aqueous solutions of iron nitrate, barium nitrate and potassium hydroxide by utilizing a continuous flow type supercritical water crystallization method. The influence of stoichiometry (Fe/Ba mole ratio) and alkalinity (R) on the product composition and morphology was studied under fixed temperature, pressure and residence time. Experiments were performed with varying Fe/Ba mole ratios and alkali mole ratio (R). Within mole ratio ranges of 0.5