The kinetics of the reaction of goethite (a-FeOOH(s)) and barium hydroxide (Ba(OH)2) in an alkaline solution to produce BaO-6Fe2O3by the hydrothermal method was investigated in the present study. The reaction was carried out in a batch closed reactor under high temperature and high pressure. The effects of α-FeOOH(s), Ba(OH)2and NaOH concentrations in the feed and the temperature on the reaction rate were examined. It was found that the reaction rate was highly dependent upon the concentration of Fe(OH)4(aq) (i.e., the dissolved a-FeOOH(s)) and Ba(OH)2. A kinetic model, based on the homogeneous phase reaction, was built to describe the dissolution of a-FeOOH(s) and the precipitation of the dissolved α-FeOOH(s) (or Fe(OH)4(aq)) and Ba(OH)2in sequence to produce the desired product, BaO.6Fe2O3. The reaction rate at 280°C is expressed as function of Fe(OH)4(aq) and Ba2+concentration.