This paper developed an output-feedback control system for regulation of continuous stirred tank reactors (CSTRs) with van de Vusse reaction. The reactors are often used as benchmark representatives of nonminimum-phase processes. Control of such nonlinear processes is difficult because they exhibit the inverse response. Linear controllers usually give unsatisfactory results in this case and thus nonlinear control approaches are more suitable. The proposed control system consists of a nonlinear observer and an extended nonlinear state feedback controller. The extension consists in adding the integrator to the controller for improving steady state performance of the control system. Stability of the control system including the observer dynamics is guaranteed, thanks to the existence of an input-to-state Lyapunov function. Simulation studies are conducted to illustrate the effectiveness of the proposed control system and its robustness. (c) 2012 Elsevier Ltd. All rights reserved.