We report an adaptive iris using dielectric liquids and a radial-interdigitated electrode. A black liquid is confined by a circular gasket with a donut shape. The surrounding of the black liquid is filled with an immiscible liquid. In the relaxing state, the black liquid obtains the largest clear aperture. By applying a voltage, the surface of the black liquid is stretched by the generated dielectric force, resulting in a reduction of its aperture. For the demonstrated iris, the diameter of the aperture can be changed from ∼4.7 mm to ∼1.2 mm when the voltage is applied from 0 to 70 V(rms). The aperture ratio is ∼94%. Owing to the radial-interdigitated electrode, the aperture size of the iris can be effectively switched with a reasonably fast response time. The optical switch is polarization-insensitive. The potential applications of our iris are light shutters, optical attenuators, biomimicry, and wearable devices.