Michael Rennie
Klaatu, alias Mr. Carpenter

Patricia Neal
Helen Benson

Billy Gray
Bobby Benson

Sam Jaffe
Prof. Jacob Barnhardt

Hugh Marlowe
Tom Stevens

Lock Martin
Gort

Freeman Lusk
General Cutler

Edith Evanson
Mrs. Crockett, landlady

Frank Conroy
Mr. Harley, Secretary to the President

Frances Bavier
Mrs. Barley, boarder

John Brown
George Barley, boarder

Olan Soule
Mr. Krull, boarder

Harry Lauter
Lieutenant in Charge of Landing Site

Robert Osterloh
Army Examining Doctor

Tyler McVey
Brady

House Peters Jr.
M.P. Captain at Barnhardt's

George Lynn
Conference Colonel Ryder

Dorothy Neumann
Margaret, Tom's secretary

Wheaton Chambers
Mr. Bleeker, jeweller

Carleton Young
Zone Five Lieutenant Colonel

Harry Harvey
The Cab Driver

Sammy Ogg
Sammy, boy witness

Bess Flowers
Lady Outside Jewelry Store

James Seay
Government Man

Stuart Whitman
Sentry (scene deleted)