Hans Conried

Narrator / Horton / Dr. H. Hoovey (voice)

June Foray

Jane Kangaroo / Mother Who / Baby Who / Cindy Lou Who (voice)

Chuck Jones

Junior Kangaroo / Various Whos / Quizmo McKwoff / JoJo (voice)

Thurl Ravenscroft

Wickersham Brother (voice) (uncredited)