Abstract: The round window placement of a vibratory transducer is a new approach for coupling an implantable hearing system to the cochlea. To evaluate the vibration transfer to the cochlear fluids and partition in response to normal acoustic stimulation and to mechanical stimulation of the round window, an acoustic-structure coupled finite element (FE) analysis was conducted by utilizing recently developed FE model which consists of the external ear canal, middle ear and cochlea. The middle ear and cochlear transfer functions such as the sound pressure gain across middle ear, intracochlear pressures, as well as basilar membrane vibration, were derived, during normal forward sound stimulation as well as reverse RW stimulation. The present results show that the round window stimulation with a harmonic pressure produces basilar membrane response similar to normal forward sound stimulation. Then a model was proposed to calculate the force required of an actuator at the round window to produce a basilar membrane displacement that is equivalent to a stimulus produced in normal ear by a given external ear-canal pressure. The information is essential for supporting the optimization of the actuators and adapting existing prostheses specifically for round window stimulation in order to insure sufficient acoustic output.