This letter reports a thermally actuated liquid microlens. In this design, a thermoelectric device was brought into direct contact with water to alter the water temperature and drive the lens through the thermal expansion of water. The shape of a pinned water meniscus at an aperture was deformed in response to the net volume change in the water, creating a tunable lens with a fast thermal response time of 0.8 s. Focal length of the microlens varied continuously from −82 mm to −29 mm as the temperature was increased from 20 °C to 30 °C.