Jiun-Myoi (1274 - July 10, 1345) was a priest of the Rinzai Sect from the latter part of the Kamakura period to the period of the Northern and Southern Courts. His original family name was Taira. His imina (posthumous name) was Myoi. His dogo (a pseudonym as a priest) was Jiun. His shigo (a posthumous name) was Keijitsu Seiko Kokushi. He was born in Shinano Province.
After becoming a priest and entering the Buddhist priesthood at Mt. Gochi in Echigo Province at age 15, he gained experience at Mt. Nikko in Shimotsuke Province as well as Kencho-ji Temple and Engaku-ji Temple in Kamakura.
He practiced Zen meditation under Jokin KEIZEN at Eiko-ji Temple in Noto Province, and later made a thatched hut at Mt. Futakami in Etchu Province
He studied under Kakumyo KOHO and accompanied his visit to Kakushin MUHON in Kii Province. After Kakushin died in 1298, he accompanied Koho's visit to Unju-ji Temple in Izumo Province, where he was certified for enlightenment. When he was residing at Tosho-ji Temple (present-day Kokutai-ji Temple (Takaoka City)) on Mt. Nijo in 1327, he responded to Emperor Godaigo's request for advice. To honor his achievement, the Emperor gave sie purple Buddhist priest stole), and the pseudonym of Seisen Zenji to Jiun-Myoi, and designated Kokutai-ji Temple as a temple under government by the Emperor's own handwriting. In his later years, Emperor Komyo also gave him another sie to honor his advice concerning Zen. The Emperor Komyo gave the pseudonym of 'Keijitsuseiko Zenji' after his death.