Ruth Underwood (born Ruth Komanoff, May 23, 1946) is a retired professional musician, best known for playing xylophone, marimba, vibraphoneand other percussion instruments in Frank Zappa and the Mothers of Invention.

Underwood played with Frank Zappa‘s Mothers of Invention from 1967 to 1977.

Underwood began her music training in the classical tradition, studying both at Ithaca College under Warren Benson and under Saul Goodman at Juilliard. Throughout 1967, she kept a regular attendance at the Garrick Theater in New York City when Frank Zappa and The Mothers of Invention was the resident band, resulting in her association with Zappa beginning in December 1967.