Brian Donlevy as Prof. Bernard Quatermass

Richard Wordsworth as Victor Carroon

David King-Wood as Dr. Gordon Briscoe

Jack Warner as Inspector Lomax

Margia Dean as Judith Carroon

Maurice Kaufmann as Marsh

John Wynn as Detective Sergeant Best

Harold Lang as Christie

Lionel Jeffries as Blake

Thora Hird as Rosie Wrigley

Sam Kydd as Police Sergeant Questioning Rosie

Gordon Jackson as BBC TV producer

Jane Asher as Little Girl (uncredited)

Toke Townley as The Chemist (uncredited)

Margaret Anderson as Maggie (uncredited)

Eric Corrie as Maggie's Boyfriend (uncredited)

Henry B. Longhurst as George, Maggie's father (uncredited)

Ernest Hare as Crash Site Fire Chief (uncredited)

Michael Godfrey as Crash Site Fireman (uncredited)

Marianne Stone as Central Clinic Nurse (uncredited)

John Kerr as Photo Lab Technician (uncredited)

Bartlett Mullins as Zookeeper (uncredited)

Mayne Lynton as Zoo Superintendent (uncredited)

Barry Lowe as Nurse Tucker (uncredited)

Jane Aird as Mrs. Lomax (uncredited)

Molly Glessing as Mother at Zoo (uncredited)

Arthur Gross as TV Show Floor Director (uncredited)

Basil Dignam as Sir Lionel Dean (uncredited)

Donald Gray as TV Program Announcer (uncredited)

Gron Davies as Charles Greene (uncredited)

Stanley Van Beers as Ludwig Reichenheim (uncredited)

Arthur Lovegrove as Sergeant Bromley (uncredited)

James Drake as Sound Engineer (uncredited)