This paper is focused on the design of a robust controller for a catalytic fixed-bed reactor with periodical inversion of the flow direction (reverse-flow reactor, RFR). The analogy between the RFR operated at infinite switching frequency and the countercurrent reactor is the basis of the simplified mathematical model of the reactor. The control system uses dilution and internal electric heating to ensure complete conversion of the reactants and to prevent overheating of the catalyst. As the state of the system is not fully available, apart from some temperature measurements, an observer is designed and used in the control algorithm. This is a typical case of nonlinear system with uncertainties. Following the procedure described in detail by Fissore [2008. Robust control in presence of parametric uncertainties: observer-based feedback controller design. Chemical Engineering Science, in press, doi:10.1016/j.ces.2007.12.019.], the extended model for the process is setup, thus taking into account all the simplifications of the model and linking performance and robustness to the control law, which is a simple state feedback. Simulations with randomly varying feeding concentration have been carried out in order to demonstrate the effectiveness of the proposed control system. (C) 2007 Elsevier Ltd. All rights reserved.