Two Tank Conical Interacting (TTCIS) is a non-linear MIMO system (i.e. level process). The process industries require liquids to be pumped as well as stored in tanks and then pumped to another tank. Most of the time the liquid will be processed by chemical or mixing treatment in the tanks, but the level of the liquid in the tank to be controlled at some desired value and the flow between tanks must be regulated. The interactions existing between loops make the process more difficult to design PI/PID controllers for MIMO processes than that for single input single output (SISO). Two input two output, TTCIS is described in the work. Here, a method for controlling multivariable processes is presented. The controller design is divided into two parts: firstly, a decoupling matrix is designed in order to minimize the interaction effects. Then, the controller design is obtained for the process + decoupler block. The aim is to meet the design specifications for each loop independently. A conventional PI controller is to keep the liquid levels in the tanks at the desired value.