This study was aimed to investigate the effect ofCyclosporin A administration on renal calcium oxalate binding under hyperoxaluric condition. Cyclosporin A administration or ammonium oxalate treatment increased calcium oxalate binding, which was further increased in kidney treated with cyclosporin A and ammonium oxalate together. The increase of calcium oxalate binding was associated with lipid peroxidation as well as with a concomitant decrease in total thiol in both rat and human kdiney homogenate. Cyclosporin A administration to hyperoxaluric rats resulted with increased calcium oxalate binding protein. However there was no change with specific activity of the protein. In conclusion, Cyclosporin A administration either to normal or hyperoxaluric rats is resulted with increased concentration of calcium oxalate binding protein as well as enhanced activity due to membrane lipid peroxidation.