Mixing is a major process in process industries, and uniformity mixture and concentration control are essential in the mixing process. This paper discusses solid ratio control of slurry in a mixing tank. In the process, powder and liquid raw materials are continuously fed to the mixing tank, and slurry is discharged from the tank after mixing. This process requires not only solid ratio adjustment but also level control. The manipulated variables of the mixing process are solid and liquid raw material feed flow rates. When a wide-range operation is required, such as during start-up, adjustment of solid ration takes a long time because the controlled and manipulated variables interfere, and the process has nonlinear dynamics. Therefore automatic control is desired. However, it is difficult to achieve smooth and quick automatic control in wide range operation by using traditional means. On the other hand, nonlinear control is effective for nonlinear process control in wide-range operation. However, selection of an appropriate theory and implementa-tion technique is essential to apply nonlinear control in accordance with the process characteristics. For the process dynamics discussed here, a rigorous model can be derived from first principles. Therefore, the feedback linearization was selected as an appropriate technique and applied to the design of a controller of a 2-input 2-output system. In ad-dition, a controller with an integral element and a method to design control parameters were also proposed in order to eliminate the steady-state error caused by disturbances, such as flowrate measurement errors. Furthermore, a method to simplify the controller for implementation in a DCS was also proposed. Through the control simulation, the con-trolled response with the simplified controller showed satisfactory performance with an appropriate setting of the time constants for the reference models.