Water hydraulic servo system is an attractive system source for its environmental safety. In this system, the problem for precise control is the uncertainties and/or the unmodeled dynamics which includes parameter variations depending on driving conditions and nonlinearity of system e.g. friction force, flow equation and so on. In this paper, we discuss the control performance of adaptive positioning controller for water hydraulic servo cylinder. This controller method aims to reduce the tracking error tend to zero for given reference signal asymptotically and ensures controller parameters keep being bounded. Based on the least square method, parameter update law is given and adaptive tracking controller is constructed. The robustness is examined experimentally for supply pressure changes and load fluctuations.