The kinetics of reduction of ferrous oxide with hydrogen were studied in a 1%-in. diameter isothermal batch fluidized reactor. The effects of mass velocity and pressure on the reduction path were investigated over the ranges 5.3 to 19.2 moles/sq.ft.hr. and 1.3 to 5.4 atm. at 1,OOO" and 1,300OF. The results are correlated by means of instantaneous oxygen balances on the assumptions that there are no oxygen concentration gradients in the solid phase, that the distribution of residence times for the gas flow is represented closely by assuming complete mixing, and that the reduction rate is controlled a t the oxide-metal interface. The rate of reduction increased with increasing pressure and mass velocity. An excellent correlation was obtained for the program a t 1,OOO'F. At 1,300OF. sintering and grain growth of the product Ioyer complicated the reduction process, and a correlation was not obtained. Application of the results to the design of commercial fluidized-reduction processes is discussed qualitatively.