The aerial oxidative precipitation and kinetics of oxyhydroxide formation from aqueous solution of ferrous sulfate with KOH as a precipitant have been studied. The influence of air flow rate, reaction temperature and initial mole ratio, R_o=[Fe²⁺]_o/[OH^-]_o, on the morphology and oxidation rate of oxyhydroxide particles and kinetics of seed formation are investigated by free pH drift and static pH experiment. The results show that the increase of air flow rate, reaction temperature and initial mole ratio increases the oxidation rate through the seed formation and seed growth on the free pH drift experiment. Needle-like α-oxyhydroxide particle of submicron size was obtained. When R_o value was decreased the particle was grown to longitudinal direction. The activation energy of seed formation is 11.71KJ/mol and rate equation of seed formation can be written as follows:
-d[Fe²⁺]/dt=1.69×10⁴[F_o2]^0.56[OH^-]^1.71exp(-11.71/RT)