To provide an agent having the actions of treating or preventing kidney disease or protecting the kidney.SOLUTION: It is found out that D-serine has, in a kidney disease mode, an action of treating kidney disease through the effects of protecting and inhibiting inflammation of the kidney, and inhibiting inflammatory cell death, and has an action of recovering the kidney functions.SELECTED DRAWING: None【課題】腎臓病の治療又は予防、又は腎臓の保護作用を有する薬剤の提供。【解決手段】D-セリンが、腎臓病モデルにおいて、腎臓の保護作用・炎症抑制作用、及び炎症性細胞死抑制作用による腎臓病の治療効果、腎機能の回復効果を見出したことによる。【選択図】なし