A flow rate control valve using a piezoelectric element has been investigated. The valve has a horn and a ball (diameter : 4mm) which are vibrated by the piezoelectric element. The liquid flow rate is controlled by the valve-opening time. The element is effective for decreasing the time required for valve open in order to supply a voltage when the pulse width is increased. Flow rate increases linearly when the pulse width is increased. The minimum pulse width is 0.4ms, which is smaller than the 1ms-width minimum for a valve using a solenoid coil.