In this work, the shaft furnace reactor of the MIDREX(R) process is simulated. This is a counter current gas-solid reactor, which transforms iron ore pellets into sponge iron. Simultaneous mass and energy balance along the reactor leads to a set of ordinary differential equation with two points boundary conditions. The iron ore reduction kinetics was modelated with the unreacted shrinking core model. Solving the ODE system allows to know the concentration and temperature profiles of all species within the reactor. The model was able to satisfactorily reproduce the data of two MIDREX(R) plants: Siderca (ARGENTINA) and Gilmore Steel Corporation (U.S.A.). Also, it was used to explore the performance of the reactor under different operating conditions. This capacity could be used for design and control purpose. (C) 2004 Elsevier B.V. All rights reserved.