This paper presents an efficient technique to design dynamic feedback control scheme for single-link flexible manipulators. A linear model can be derived for the robotic system using the assumed-mode method. Conventional techniques such as pole-placement or LQR require physical measurements of all systme states, posing a stringent requirement for its implementation. To overcome this problem, a low-order state functional observer is proposed here for reconstruction of the state feedback control action. The observer design involves solving an optimisation problem with the objective to generate a feedback gain that is as close as possible to that of the required feedback controller. A condition for robust stability of the closed-loop system under the observer-based control scheme is given. The attractive features of the propsed technique are the resulted functional state observer is of a very low order and it requires only sensor measurements of only the output- the tip position of the arm