We present a fuzzy approach to design a robust suboptimal control for decentralized interconnected system. We denote the non-linear interactions between the sub-systems are uncertain and in many real-life situation it can be represented by the differences of actual behavior from nominal description of sub-systems (e, é). Fuzzy sliding mode control is designed hr sub-system to track the prespecified trajectory in phase plane (e, é) according it’s states (x,x´). Fuzzy adaptation is proposed for tuning closed-related control subsystem on the sliding surface toward new equilibrium points. The adaptation strategy is determined by rule bases based on considering controller as PID controller with variable structure, switching between different PID settings with different inputs (e, é).