ラ行變格活用（ラ行変格活用）係日文古文文法中動字活用嘅一種，講嘅係活用詞尾以五十音圖嘅ラ行 (ra， ri， ru， re， ro)音為基礎發生唔規則嘅變化，簡稱為「ラ変」。有呢一種活用嘅詞淨係得「有り」「居（を）り」「侍（はべ）り」「いまそかり（いますがり）」呢四個詞啫。
ラ行 declension (ラ行変格活用) is a kind of verb active use in ancient Japanese grammar, which refers to the irregular change of the end of the word based on the ラ行 (ra, ri, ru, re, ro) sound of the fifty-syllable diagram, referred to as "ラ変". There are only four words that can be used in this way: "有り", "居 (を)り", "侍 (はべ)", "いまそかり (いますがり)".