This paper reports a two-dimensional vector velocimeter on the basis a the time-varing spatialfiltering method using a rotating disk with two transmission gratings. The filtering characteristics ofthe spatial filter employed in the practical experiment were studied theoretically. The velocimeter isused to measure the flow velocity of water in a small glass pipe. The flow velocity was measured inreal time by using a new signal analizing system. The experimental resurts show the usefulness ofthe proposed velocimeter for the measurements of flow velocities.