This paper studies the problem of designing a robust controller for the nonlinear multi-input multi-output continuous stirred tank reactor (CSTR) in the presence of uncertainties in parameters of the process model. For this purpose, by first using the feedback linearization method, the equivalent linearized model of the CSTR is obtained. In the second step, to cope with uncertainties, two robust controllers are designed; one using H mixed-sensitivity and the other using DK-iteration method. In this step, the required performance and uncertainties are expressed in terms of the suitable weight functions. Finally, the performance of the resulting feedback system is verified through numerical simulations.