An adaptive liquid iris for an optical switch based on electrowetting is demonstrated. The device consists of a clear conductive liquid and an opaque insulate oil. In the voltage-off state, the dome of the clear liquid touches the top substrate, and an iris-like opening is formed in its central area, and the aperture of the opening is at its largest. When a voltage is applied to the device, the shape of the conductive liquid is deformed due to the electrowetting effect. As a result, the diameter of the opening is reduced. Our results show that the aperture of the device can be tuned from ∼6.4 mm to 0 as the applied voltage is changed from 0 to ∼60 V . The device can obtain a high optical attenuation (∼872∶1 ). The response time was measured to be ∼117 ms (shrinking time is ∼25 ms , and relaxing time is ∼92 ms ) with turnaround speed of 55 mm/s . Our device has potential applications in light shutters, variable optical attenuators, adaptive irises, and displays.