Japan absorbed Tang culture including Chinese Buddhist Sūtras through envoys in the Nara period. The copies of Baoyu jing (Treasure Rain Sūtra寶雨經) were also written based by those imported texts as part of Tripitaka so-called Gogatsu tsuitachi kyō (五月一日經) executed by the Empress Komyō (光明皇后). Baoyu jing had been regarded to be an important Buddhist authority proclaiming the justice of Empress Wu. Interestingly enough, those Japanese copies include Chinese modified characters of Empress Wu (則天文字), though this fact has hitherto received no scholarly attention. It is important enough that Baoyu jing copies were also found in Dunhuang and Turfan. As Empress Wu characters were submitted five times, by examining their usage, we can found out that the original of these copies were transcribed just in one year after its translation. This fact provides the possibility that the Imperial Court had produced those copies as standardized texts and distributed them throughout the land.