In Royal College of Surgeons (RCS) rats with inherited retinal dystrophy, photoreceptor cell degeneration is accompanied by Muller cell changes, in particular, increased expression of the intermediate filament protein, glial fibrillary acidic protein (GFAP). In this study, we examined the expression of GFAP in retinas of 4 month-old RCS dystrophic rats either transplanted with normal retinal pigment epithelial (RPE) cells or injected with vehicle (sham control). The sham-injected and non-treated retinas showed increased expression of GFAP in Muller cells with advancing age. GFAP-immunostained Muller processes were observed in the region of the subretinal space of these RCS retinas beginning by 4 months. However, in the retinas of RCS rats transplanted with normal RPE cells, GFAP expression by Muller cells was significantly reduced. Specifically, under the transplanted RPE cells, GFAP-inununolabeled Muller radial processes were not observed and GFAP immunostaining was not present in the subretinal space at any time period examined. Immunoblot analysis of the superior hemisphere of RPE-cell transplanted retinas of 4 month-old RCS dystrophic rats showed less GFAP immunostaining than sham-injected and the inferior hemisphere of retinas of age-matched RCS rats. This study showed that in normal RPE-cell transplanted retinas of RCS rats, in addition to rescued photo-receptor cells, there was an accompanying stabilization of Muller cells as demonstrated by a reduction in the expression of GFAP.