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This paper describes the design and development of a small actuator using a miniature piezoelectric stack and a flextensional mechanical amplification structure for an implantable middle ear hearing device (IMEHD). A finite-element method was used in the actuator design. Actuator vibration displacement was measured using a laser vibrometer. Preliminary evaluation of the actuator for an IMEHD was conducted using a temporal bone model. Initial results from one temporal bone study indicated that the actuator was small enough to be implanted within the middle ear cavity, and sufficient stapes displacement can be generated for patients with mild to moderate hearing losses, especially at higher frequency range, by the actuator suspended onto the stapes. There was an insignificant mass-loading effect on normal sound transmission (<;3 dB) when the actuator was attached to the stapes and switched off. Improved vibration performance is predicted by more firm attachment. The actuator power consumption and its generated equivalent sound pressure level are also discussed. In conclusion, the actuator has advantages of small size, lightweight, and micropower consumption for potential use as IMHEDs.