A novel decentralized PID controller design procedure based on backstepping principles is presented to operate multiple-input multiple-output (MIMO) dynamic processes. The first key feature of the design procedure is that a whole MIMO control system is decomposed into multiple control loops, therefore the sub-controllers can be efficiently flexibly designed in parallel prototype. The second key feature is that the decentralized controller has equivalency to those designed by backstepping approach. As a complementary support to the design procedure, the sufficient condition of the whole closed-loop system stability is analyzed via the small gain theorem and it can be proven that the process tracking performance is improved. The simulation results of the Shell benchmark control problem are provided to verify the effectiveness and practicality of the proposed decentralized PID control. 1 Introduction Decentralized PID control [1,2] for MIMO processes is popular in the chemical and process indus-tries because of its relatively simple structure and fewer tuning parameters. In addition, controller design focuses on single control loop and has little affect on other control loops, which is convenient to maintenance and amendment. However, the tuning procedure often involves trial and error experiments and requires an experienced operator, which is time consuming. With respect to the structural feature of decentralized control, there are some rules in PID controller s parameters tuning for the adjustment of controller and the performance analysis of the control system. [3] and [2] presented effective de-centralized PID control algorithms for interacting two-input two-output (TITO) and MIMO processes, respectively, however, they all lack the stability analysis. Backstepping [4] is a recursive and systematic design scheme first presented by Kokotovic in 1991. Its designing idea is to decompose a complex system into multiple small-scale subsystems, then to design recursively control Lyapunov function (CLF) [5] and virtual control variable for each subsystem, and finally to obtain the original control law, realizing the global regulation and tracking for a class of feedback linearizable nonlinear systems [6] . Some researches have been focused on the application of backstepping method to decentralized control. [7] proposed an adaptive backstepping-based scheme for designing a totally decentralized adaptive stabilizers for a class of large-scale systems with guaranteed transient performance. Unfortunately, the industrial PID control application examples of backstepping method are very few [8∼9] . [8] developed a backstepping-based adaptive PID control scheme that the robustness and transient performance are better than those of the conventional PID control. Therefore, combining backstepping with decentralized PID control will be of great theoretical and applicable value. Decentralized PID controller design scheme and procedure are proposed for MIMO processes on the basis of backstepping approach. MIMO processes are decomposed into multiple loops and controllers are designed in parallel. First, CLF and virtual control variable based on backstepping are derived recursively for each loop and a multivariable controller can be obtained. Then, a decentralized PID controller can be derived via selection of the auxiliary control variable. By introducing small gain theorem the sufficient condition of the whole closed-loop system stability is acquired and the tracking performance is improved. The simulation study of the Shell benchmark control problem illustrates that the decentralized PID control scheme is effective for MIMO processes.