Dr. Russell A. Marvin
Hugh Marlowe
Carol Marvin
Joan Taylor
Motorcycle cop
Larry J. Blake
Air Intelligence Command Officer
Bert Stevens
Military Officer at Experiment
Forbes Murray
Officer/Civilian at Military Conference
Arthur Tovey
Major Kimberly
Alan Wells
Military Officer at Experiment (uncredited)
Nicky Blair
Military Messenger (uncredited)
Jimmy Cross
Military Officer (uncredited)
Jack Deery
Dr. Alberts (uncredited)
Charles Evans
Military Official (uncredited)
Raoul Freeman
Maj. Huglin
Donald Curtis
Alien (voice) (uncredited)
Paul Frees
James Gonzalez
Minor Role (uncredited)
Duke Green
Ed Haskett
Sgt. Nash (uncredited)
Clark Howat
Cutting - Generator Technician (uncredited)
Harry Lauter
Don Marlowe
Worker in Control Tower (uncredited)
William Meader
Plane Passenger (uncredited)
Sol Murgi
Brig. Gen. John Hanley
Morris Ankrum
Radio Listener (archive footage) (uncredited)
William J. O'Brien
Murray Pollack
Tank Commander (uncredited)
Mike Ragan
Maj. Kimberly (uncredited)
Alan Reynolds
Man Crushed Beneath Wall (uncredited)
Dale Van Sickel
Civilian Observing Saucer Attack (uncredited)
Guy Way
Bob Whitney
Alfred Cassidy (uncredited)
Frank Wilcox
Chinese Radio Listener (uncredited)
Beal Wong
Narrator (voice) (uncredited)
William Woodson
Vice Adm. Enright
Thomas Browne Henry
Gen. Edmunds
Grandon Rhodes
Prof. Kanter
John Zaremba
Alien (voice)
Alfred Cassidy
Frank the garage man
Sydney Mason
Producer
Charles H. Schneer
Director
Fred F. Sears
Executive Producer
Sam Katzman
Visual Effects
Ray Harryhausen
Screenplay
George Worthing Yates
Novel
Donald E. Keyhoe
Screenstory
Curt Siodmak
Bernard Gordon
Unit Manager
Leon Chooluck
Special Effects
Russ Kelley
Art Direction
Paul Palmentola
Editor
Danny B. Landres
Assistant Director
Gene Anderson Jr.
Director of Photography
Fred Jackman Jr.
Set Decoration
Sidney Clifford
Sound
J.S. Westmoreland
Production Coordinator
Jack Erickson