Like other systems, robot control systems are subjected to external disturbances and noises, which usually decrease stability and performance. An issue in robot control is existence of uncertainty which usually depends on the robot work conditions. Working in unknown environment such as underwater environments and the absence of exact model of external forces such as drag or added mass cause structural uncertainty in robot models. In some of applications such as welding or cutting, the robot manipulator is in contact with its surrounding environment which produces a force to the robot manipulator. On the other side, with respect to robot working conditions, an observer may be used for estimating some of state variables and a controller is designed based on this observer to reduce the number of sensors. With respect to work conditions and need to high load to power ratio, using hydraulic actuators may be preffered to electromechanical actuators. In this thesis, at first a velocity observer is designed for series manipulators, then, a position controller is designed and simulated based on this observer for series linear hydraulic manipulators with pressure control valves. Furthermore, another observer is designed based on using force sensor for series robots, then, a robust impedan ce controller is designed and simulated based on this observer. In all cases, stability of the observers is proved and stability of the whole control systems is guaranteed using Lyapunov stability theory. Simulations are executed in the presence of position measurement noise and input external disturbances. Results show the very good performance of the observer and controller. In case of force control, simulation shows that the performance of the robot control system is highly affected by the noise. Keyword: Robust Impedance Controller, Hydraulic Manipulator, Servo Hydraulic Actuator, Underwate Manipulator, Velocity Observer.