A polymer V-shaped electrothermal actuator (ETA) array that is capable of compressing a live biological cell with a desired strain was designed, fabricated and characterized. This polymer electrothermal array is the core of a microelectromechanical systems (MEMS) device to measure the mechanical compliance of a cell. A polymer electrothermal actuation mechanism was selected because it is able to operate in an electrolytic solution (cell medium), which was needed to keep cells alive during testing. The MEMS-based device was optimized utilizing finite element analysis and the devices were fabricated using surface micromachining techniques. Characterization of these devices was conducted in air, deionized water and cell mediums. Operating these devices in liquid environments was performed using direct current voltages less than 2.0 V or high-frequency (800 kHz) alternating current voltages. The actuator displacement was up to 9 µm in air and 3 µm in liquids, i.e. it achieves 30% displacement of that in air when operating in liquids. Such remarkable performance is due to the large coefficient of thermal expansion and low thermal conductivity of the structural polymer (SU-8). Finally, we demonstrated the suitability of this actuator for biological applications by compressing a cultured NIH3T3 fibroblast in the cell medium.