The Vibrant Soundbridge (VSB, Med-El, Austria) is a semiimplantable hearing aid usually attached to the long process of the incus to vibrate the ossicular chain in patients with moderate to severe mixed hearing loss. We implanted a VSB vibratory transducer on the round window membrane of the left ear in two cases not treated effectively by tympanoplastic surgeries. Pure tone audiography did not differ significantly in the two cases pre- or postoperatively, indicating that the small mass transducer does not adversely affect middle-ear vibration. Postoperative hearing thresholds with VSBs were similar to those when patient 1 wore an air-conductive hearing aid and patient 2 wore a bone-anchored hearing aid (BAHA). VSB implantation on the round window could thus potentially benefit many patients with mixed hearing loss.