カ行變格活用（日文：カ行変格活用）係日文古文文法當中動字活用嘅一種，講嘅係活用詞尾以五十音圖嘅カ行 (ka， ki， ku， ke， ko)音為基礎發生唔規則嘅變化，簡稱為「カ変」。有呢一種活用嘅詞淨係得「來る（くる）」（古文中得「來（く）」）呢一個詞啫。
カ行 declension (Japanese: カ行変格活用) is a kind of verb used in ancient Japanese grammar, which refers to the irregular change of the ending of the active word based on the sound of ka, ki, ku, ke, ko, etc. There is such a word that is used only by the word "来る (くる)" (in ancient Chinese for "come (く)").