This paper presents an adaptive control of a piezoelectric actuator based flexible arm with unknown and unmeasurable disturbances. In real systems with external disturbances and dynamics of actuator, the vibration effect due to the inherent elastic deformation of flexible arm makes the satisfactory control results unachievable. To reduce the vibration effect and to consider the actuator dynamics based on an external disturbance model with consideration of dynamics of a piezoelectric actuator, adaptive vibration control experimental system is designed, where the controller is based on Youla-Kucera parametrisation and right coprime factorisation. Robust analysis of the proposed control system is also shown. As a practical appeal, simulation and experimental results are shown to support the proposal on the control system design.