Kayo Matsuo is a Japanese voice actress born on March 5, 1944, in Tokyo. She is affiliated with the agency Sigma Seven. Her career as a voice actor began in the mid-1960s, and during the 1960s and 1970s, she was frequently cast in leading female roles. In her later career, she became known for playing elderly women as well as young boys, often using a lower vocal register for these parts.

Matsuo has an extensive list of anime credits spanning several decades. She is recognized for voicing Marco Rossi in the classic series 3000 Leagues in Search of Mother (1976) and Flora Robinson in The Swiss Family Robinson: Flone of the Mysterious Island (1981). Another significant role was the Great-Grandmother (Ametsuchi Akino) in the ARIA series from 2005 to 2008. Her other television animation work includes parts in The Adventures of Tom Sawyer (Bennie Thayer), Anne of Green Gables (Lucilla Harris), Mighty Atom, Galaxy Express 999, The Gutsy Frog, City Hunter, Case Closed, and the World Masterpiece Theater productions of Dog of Flanders and A Dog of Flanders.

In addition to her television work, Matsuo has voiced characters in animated films and original video animations (OVAs). Her film roles include the theatrical features Doraemon: Nobita and the Kingdom of Clouds and xxxHOLiC: A Midsummer Night's Dream. She has appeared in OVAs such as ARIA The OVA: Arietta and the Legend of the Galactic Heroes series. Her work in video games includes roles in the ARIA: The Natural Mirage of Distant Memories and Super Robot Wars series, as well as voicing Kamen for the game Hyakutong no Ares. Her other contributions to the industry include narration for programs like Super J Channel and work for the Tokyo National Museum.

Matsuo has recurring collaborations with other notable voice actors, including performing alongside Nobuyo Oyama and Masato Mori in the Super Robot Wars series and the anime Zambot 3. She is also recognized for her live-action role as Sayaka Yagyu in the 1972 film Lone Wolf and Cub: Baby Cart at the River Styx.