This paper describes an adaptive speed control scheme for a pneumatic servo system which is composed of an axial piston motor and an electro-pneumatic proportional valve. The features of the adaptive control scheme are that it is applicable to non-minimum phase systems and that its structure is as simple as the MRAC.<BR>Experiments of the adaptive speed control were carried out for several conditions, and their results were compared with those of the conventional PI-D control. From the experimental results summarized below, the effectiveness of the proposed scheme was confirmed : <BR>(1) Three sampling periods (T_s=36, 71, 106msec) were tested, and the stability of the adaptive control system was confirmed for each Ts even through the identified plant model was non-minimum phase. The steady state error was not influenced by T_s, and its maximum value (±1.0rpm) was smaller than that of PI-D control (±2-±2.5rpm) for a reference speed larger than 300rpm.<BR>(2) The second order reference model was used to specify the wave-form of the step response, and good tracking performance was obtained for several damping coefficients and natural frequencies. The distortion of the step response for large amplitude inputs was much smaller than that of PI-D control.<BR>(3) A sudden change of the load torque or supplied air pressure was applied to the control system as a disturbance. The speed fluctuation was much the same as that of PI-D control.