І. Background: Prolonged excessive salt intake is an important risk factor for development of renal fibrosis. In the onset of renal tubular destruction, KIM-1 appears in urine. CHOP is an important apoptosis stimulator protein. The aim of present study was to investigate the effect of high salt diet in development of renal fibrosis through apoptosis.ІІ. Methods and results: The 25 male Wistar rats were divided randomly into five groups and treated with 0%, 0.5%, 1%, 1.2%, 1.5% of NaCl dissolved

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... in distilled water for 8 weeks. For confirmation of renal tubular destruction, the urinary KIM-1 was measured. The slides of renal tissue were prepared and stained with Hematoxylin and Eosin and Masson´s Trichrome for fibrosis detection. To investigate the role of CHOP protein in development of renal tubulointerstitial destruction, the relative gene expression of CHOP in renal tissue was analyzed using qRT-PCR method.There was no significant differences in urea, creatinine and total protein concentration of rats received different concentrations of NaCl compared to the control group. Urinary KIM-1 and mRNA level of CHOP was found to be increased significantly in rats treated with 1.5% NaCl compared to the control group. Mild renal fibrosis was observed in the same group too.III. Conclusion: Excessive salt intake can lead to fibrosis through increasing the expression of apoptotic CHOP gene in renal tissue. KIM-1 can be detectable in urine long before the development of renal fibrosis.