An object of the present invention is to provide a combination drug that has remarkably excellent preventive and/or therapeutic effects on polycystic kidney disease. The present invention provides a drug for preventing and/or treating polycystic kidney disease comprising a combination of tolvaptan or a prodrug thereof with a somatostatin derivative, and a method for treating polycystic kidney disease using this drug.本發明之目的係提供一種用於多囊性腎臟病具有顯著優異的預防及/或治療效果之組合藥物。本發明提供一種用於預防及/或治療多囊性腎臟病之藥物,包含托伐普坦(tolvaptan)或其前藥與生長抑制素衍生物的組合,及一種使用此種藥物以治療多囊性腎臟病之方法。