An integrated variable-focusing microlens chip with thermal actuator and sensor, which is capable of adjusting its focal length over a wide range, is reported. The packaged microlens chip consists of a flexible polymer lens, a thermal actuator, and a sensor. The focal length change is controlled by varying the voltage applied to the thermal actuator and without any mechanical moving parts. The focal length varies from 9.197 to 2.619 mm, which corresponds to the change of numerical aperture from 0.146 to 0.448. Potential applications include the camera phone, surveillance camera, disc recording systems, collimator, sensing systems, confocal imaging systems, and optical communication.