- 1931
- Born in Ibaraki prefecture.
- 1953
- Joins the Demokrato Artists association.
- 1954
- Graduates from Art Department, Faculty of Education, the Tokyo Kyoiku University (the present University of Tsukuba).
- 1955
- Founds Group Jitsuzaisha with Masuo Ikeda and others.
- 1958
- Moves to the United States. Ay-O sets up a base in NewYork thereafter and he begins going back and forth between Japan and the U.S.
- 1961
- Devotes himself to Fluxus mouvement on referral from Yoko Ono.
- 1964
- Exhibits series of Rainbow Happening as part of the Fluxus event (the Carnegie Recital Hall, New York).
- 1966
- Appeared in Allan Kaprow’s book “Assemblage, Environments & Happenings” as the early Environment artist along with Yayoi Kusama and George Segal.
Represented Japan at the 33rd Venice Biennale. - 1971
- Represented Japan at the 11th Sao Paulo Biennale in which he receives Brazil Bank Prize.
- 1987
- Suspends a 300 meters long rainbow banner from the Eiffel Tower in Paris
- 1995
- Receives a Prize Purple Ribbon
- 2006
- Solo show “Over the Rainbow: Ay-O Retrospective 1950-2006” (Fukui Fine Arts Museum,Fukui, Miyazaki Prefectural Museum).
- 2010
- Solo show “Ay-O 1950s-2010: Retrospective” commemorating twenties anniversary from the museum foundation(Tsukuba Museum of Art, Ibaraki).
- 2012
- Solo show “Ay-O: Over the Rainbow Once More”(Museum of Contemporary Art, Tokyo, Niigata City Art Museum, Hiroshima City Museum of Contemporary Art).