The effects of added surfactants on the size and shape of the monodispersed iron oxide particles preparedby forced hydrolysis from aqueous ferric chloride solutions were investigated by transmission electron microscopes.When the concentration of ferric chloride solutions increased, either the particle growth displayed clear delays or only areaction intermediate of β-FeOOH was made. The cation and the amphoteric surfactant formed a spherical α-Fe2O3within 12hours regardless of the added concentration, and the anion delayed the growth of its particles or simply madethe β-FeOOH as the concentration increased.