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This paper presents investigation into the development of decentralized sliding mode control with application to trajectory tracking for hydraulically driven revolute robot manipulators. The control of hydraulically actuated robot manipulator is very challenging due to the highly nonlinearities in its dynamics, uncertainties parameters, and variations on payload. To overcome these problems, an integrated mathematical model of an N degree-of-freedom (dof) hydraulic robot manipulator is treated as a large-scale uncertain system models with bounded uncertainties where the bounds are known. This is then decomposed into interconnected uncertain subsystems in order to apply the decentralized tracking control strategy. Sliding mode control (SMC) and proportional-integral sliding mode control strategies will be utilized to overcome the inherent nonlinear dynamics under the decentralized frameworks. These approaches were adopted to ensure the stability of the system dynamics during the sliding mode and the insensitivity to the parameter variations and disturbances. The performance and robustness of the controllers were evaluated on a 3 dof hydraulically actuated manipulator through computer simulation. The results prove that the controllers have succeeded in forcing the 3 DOF hydraulic robot manipulators to track the predefined desired trajectory at all time.