Unilateral vestibular ganglionectomy (UVG) results in a complete degeneration of vestibular nerve fibers and terminals in the ipsilateral vestibular nuclear complex (VNC). A subsequent glial reaction may affect the activities of VNC neurons and thereby influence compensation for lesion-induced vestibular disorders. Expression of glial fibrillary acidic protein (GFAP), a specific marker for reactive astrocytes, was demonstrated immunohistochemically in the rat VNC at 7, 14, and 35 days after UVG. An increased GFAP-positive astrocytic response was evident at 7 days after lesion in all the VNC regions on the lesioned side and in some regions on the unlesioned side and remained through 35 days. The glial response included hypertrophy, which was more prominent at 7 days than at 14 days or 35 days, and proliferation, more prominent at the later times, of GFAP-positive astrocytes. Astrocytic projections around VNC neuron somata and proximal dendrites increased in number and became thicker and more elongated, especially at 14 days, in the lateral vestibular nucleus. It is suggested that UVG results in a bilateral astrocytic reaction in the VNC that would affect the subsequent compensation.