The purpose of this study is to analyze the pronunciation of Er耳 during Middle Chinese period. In Guangyun廣韻 which is the standard rhyme dictionary at that time, the phonetic notation of Er is Erzhi-qie而 止切 which means the pronunciation of Ri-mu日母 Zhi-she止攝. But the different phonetic notations are found in Jiyun集韻, like Ruzheng-qie如蒸 切 and Rengzheng-qie仍拯切 which is from Guanzhong關中 dialect. Through these, the pronunciation of Er has been changed and divided into two or three different way during Old Chinese period, and these had reflected in dialect.