In metallurgical processes, fluidized-bed technology is gaining more importance because of its advantages. Processes with H-2-rich and CO-rich reducing gases were developed for the reduction of iron ore fines (e.g. FINEX (R)). For improvement of these new technologies, greater knowledge about the chemical kinetics of iron ore reduction in fluidized beds is necessary. The scope of this work is to evaluate the limiting regime of the iron ore fines reduction. Therefore, experimental results of reduction tests were compared with theoretically investigated reduction rates. These reduction rates were based on a limitation either of mass transfer through the external gas film to the particle surface, diffusion in a porous product layer (pore diffusion and Knudsen diffusion), diffusion in a dense product layer (solid diffusion) or the phase boundary reaction. The phase boundary reaction was found to be the most likely limiting reaction regime.