The collision of particles having diameter ranging from 20 to 300 mu m in a gas with a wall was studied both experimentally and theoretically. The effect of the particle diameter on the incident and rebound velocities was quantitatively examined by using images captured by a high-speed microscope camera. The incident velocities calculated using a model that takes into account the increase in fluid resistance near a wall surface, i.e., the lubrication effect, were in good agreement with the results obtained experimentally. Smaller particles had lower velocities owing to the increase in the ratio of fluid resistance to particle inertia. Experiments conducted by varying the incident velocity and particle density further indicated that the coefficients of restitution decrease with the decrease in the Stokes number.