Abstract: The friction characteristics of pneumatic cylinders are studied. A test bed to measure static and dynamic friction forces is designed using a meter-out circuit. The dynamic friction forces are tested under different supply pressure, piston velocity and differential pressure between two chambers. A friction model is obtained from the tested data. The model is valuable for the study of the stick-slip and the servo control of the pneumatic cylinders. Experiment results show that the relationship between the dynamic friction force and piston velocity takes on a quadratic form and is related to the differential pressure between two chambers.