Keisai Aoki (青木恵哉, Aoki Keisai, April 8, 1893-March 6, 1969) was a Japanese missionary who virtually paved the way to the establishment of Hansen's disease sanatorium Kunigami-Airakuen, Okinawa, now Okinawa Airakuen Sanatorium, Japan. At age 16, he developed leprosy and later, under the leadership of Hannah Riddell, he helped people with leprosy in Okinawa.
He was born in Tokushima Prefecture on April 8, 1893. His real name was Yasujiro Aoki. At age 16 he developed leprosy and everything did not help, including the pilgrimage of 88 holy places of Shikoku (at that time it was believed to be of help). In 1916 he entered the Oshima Leprosarium and was baptized in 1918. He helped with missionary work, and he sent a letter to Hannah Riddell since he was worried about women's temptation. At Kusatsu, he met Hannah who was vacationing there and decided to go to Hannah's Kaishun Hospital. He helped with missionary work. He cherished affection for Aiko Tamaki, and this worried him because this was against the Riddell's policy of sex segregation. He decided to go to Okinawa on missinary work at the strong suggestion of Riddell.