Objective To observe the influence of interleukin-1beta; (IL-1beta;) on the expression of phosphorylated signal transducers and activators of transcription 3 (pSTAT 3) in rat retinal Muuml;ller cells.Methods For in vitro study cultured Muuml;ller cells were treated with IL-1beta; of different concentrations (0, 0.1, 1, 5 and 10 ng/ml) for 24 hours. For in vivo study, 32 Sprague-Dawley（SD）rats were divided into 4 groups randomly (control group，100，500 and 1000 ng/ml group) with 8 rats in each group. After 24 hours of injection with phosphate buffered solution (PBS), or 100,500,1000 ng/ml IL-1beta; into the vitreous cavities of the above rats, retinas were harvested. The expressions of pSTAT3 in cultured Muuml;ller cells or treated retinas were evaluated by indirect immunofluorescence and western blotting.Results After 24 hours of incubation without IL-1beta;, pSTAT3 has little expression in cultured Muuml;ller cells, but was upregulated by 1 ng/ml or higher IL-1beta; in a dosagedependent manner (F=46.64, 43.78;P＜0.01). pSTAT3 was not expressed in adult rat retina, but was upregulated by vitreous injection of 100 ng/ml or higher IL-1beta; in a dosagedependent manner (F=73.53,43.70;P＜0.01).pSTAT3 expressed mainly in inner nuclear layer and ganglion cell layer. Doublelabeling showed that there was no costaining of pSTAT3 and glial fibrillary acidic protein (GFAP) in retina of control group, but there were many costained Muuml;ller cells in retinas treated with IL-1beta;.Conclusions Expression of pSTAT3 in Muuml;ller cells could be activated by IL-1beta; which may represent one pathway link to reactive gliosis.