AIM:To assess the differentiation of rat mesenchymal stem cell（MSC） in the microenvironment of retinitis pigmentosa（RP） induced by the administration of sodium iodate. METHODS:In vitro cultured Lewis rat MSC were injected into the subretinal space of NalO₃ induced RP rat eyes（30g/L NalO₃100mg/kg）.To observe the trace and differentiation of MSC by immuno-fluorescent method successively in 5 weeks after the surgery. RESULTS:The majority of the transplanted cells stay in retinal pigment epithelium（RPE） layer and cones and rods layer.From the 2^nd week after transplantation,the engrafted MSC expressed PCK and rhodopsin under fluorescent microscope. CONCLUSION:MSC can survive mainly in the outer layer of retina in the microenvironment of RP and differentiate forward the RPE cell and photoreceptor.