Baisao (Japanese: 売茶翁 Hepburn: baisaō?) (1675–1763) was a Japanese Buddhist monk of the Obaku school of Zen Buddhism, who became famous for traveling around Kyoto selling tea. The veneration of Baisao during and after his lifetime helped to popularize sencha tea and led to the creation of the sencha tea ceremony.
Baisao went by many names during his lifetime, as was common at the time. As a child, he was known as Shibayama Kikusen. When he became a monk, his Zen priest name was Gekkai Gensho. Baisao, the nickname by which he is popularly known, means "old tea seller." He acquired this name from his act of making tea in the Kyoto area. Later in his life, he denounced his priesthood and adopted the lay name of Ko Yugai.
Baisao was born in the town of Hasuike in what was then Hizen Province. His father died when he was nine years old. Baisao became a Zen Buddhist monk at Ryushinji, an Obaku temple. His teacher, Kerin Doryo, had received instruction directly from Ingen, the founder of the Obaku school. Starting in 1696, Baisao travelled extensively for several years to study at various temples in Japan. Baisao then returned to his temple and served as its steward until 1723, when Daicho Genko became its abbot. His mother also died in that year. In 1724, when Baisao was 49 years old, he left the monastery and went to Kyoto, where he would live for the remainder of his life. With letters of introduction from Daicho, Baisao quickly gained the friendship of many leading artists, monks, and literati in Kyoto.
Around 1735, Baisao began selling tea in the various scenic locations in Kyoto. At this time, he had not yet formally given up his priesthood. Baisao never sold his tea for a fixed price. Instead, he carried a bamboo tube with which he collected donations. He lived an ascetic life, despite his lasting friendships with illustrious individuals, and used the meagre donations from his tea peddling to keep himself nourished. As for his tea equipment, he carried it all in a woven bamboo basket he called Senka ("den of the sages") that he lugged around on a stick over his shoulder.