Sai On (蔡温) (1682–1762), or Cai Wen in Chinese, also known as Gushi-chan Bunjaku (具志頭 文若, lit. Bunjaku, head of Gushi), was a scholar-bureaucrat official of the Ryūkyū Kingdom, serving as regent, instructor, and advisor to King Shō Kei. He is renowned for the many reforms he initiated and oversaw, and is among the most famous figures in Okinawan history. He edited Chūzan Seifu, a rewrite of Chūzan Seikan by his father Sai Taku.