Jeffrey Hunter as Christopher Pike

Leonard Nimoy as Spock

Majel Barrett as Number One

Susan Oliver as Vina

Meg Wyllie as The Keeper

Peter Duryea as Lieutenant José Tyler

Laurel Goodwin as Yeoman J. M. Colt

Clegg Hoyt as Transporter Chief Pitcairn

Malachi Throne as The Keeper (voice)

Michael Dugan as The Kaylar

Georgia Schmidt as First Talosian

Robert C. Johnson as First Talosian (voice)

Serena Sande as Second Talosian

Jon Lormer as Dr. Theodore Haskins

Adam Roarke as C.P.O. Garrison

Leonard Mudie as Second Survivor

Anthony Jochim as Third Survivor

Edward Madden as Enterprise Geologist

Robert Phillips as Orion Space Officer

Joseph Mell as Earth Trader

Janos Prohaska as Anthropoid Ape / Humanoid Bird

Carol Daniels as Bridge Crewmember (uncredited)