- Buster Crabbe
- Flash Gordon
- Jean Rogers
- Dale Arden
- Charles Middleton
- Emperor Ming
- Frank Shannon
- Dr. Alexis Zarkov
- Beatrice Roberts
- Queen Azura
- Donald Kerr
- Happy Hapgood
- Richard Alexander
- Prince Barin [Chs. 6-15]
- C. Montague Shaw
- Clay King
- Wheeler Oakman
- Tarnak
- Kenne Duncan
- Airdrome Captain
- Warner Richmond
- Zandar
- Jack Mulhall
- Bomber Captain [Chs. 4-5, 13]
- Lane Chandler
- Flight Commander [Chs. 2-3]
- Anthony Warde
- King Turan of the Forest People [Chs. 7, 11, 13]
- Ben Lewis
- Professor [Ch. 1]
- Wheaton Chambers
- Professor
- George Cleveland
- Professor Hensley
- Priscilla Lawson
- Princess Aura - n Flashback [Chs. 6, 10, 14]
- Kane Richmond
- Pilot Captain
- Earl Askam
- Officer Torch - in Flashbacks [Chs. 6, 10, 14]
- Hooper Atchley
- Dr. Dunord [Chs. 1, 9]
- Roy Barcroft
- Martian Soldier [Ch. 2]
- James Blaine
- Prof. Richter [Chs. 1,9]
- Thomas Carr
- Captain Rama of the Forest People [Chs. 6-7 - 10-11 - 13]
- George DeNormand
- Martian Soldier [Chs. 3, 9-10]
- Earl Douglas
- Martian Soldier
- James Eagles
- High Priest of Kalu [Chs. 8, 10-11]
- Al Ferguson
- Soldier
- Jerry Frank
- Stratosled Co-Pilot [Chs. 5-6] / Relay Televisor [Chs. 7, 11] (uncredited)
- Jack Gardner
- Temple Assistant [Chs. 10-11]
- Alan Gregg
- Clay Spy [Ch. 6]
- Herbert Holcombe
- Martian Soldier
- Reed Howes
- Stratosled Pilot [Chs. 5-6]
- Reid Kilpatrick
- Radio Announcer [Ch. 1]
- Fred Kohler Jr.
- Martian Soldier
- Jack 'Tiny' Lipson
- King Vultan - in Flashback [Ch. 10]
- Theodore Lorch
- High Priest - in Flashback [Chs. 6, 10]
- Charles McMurphy
- Atom Furnace Slave Driver - in Flashback [Ch. 14]
- Louis Merrill
- Dr. Metz
- Charles Murphy
- Sergeant-at-Arms [Ch. 1]
- Eddie Parker
- Martian Soldier
- James Pierce
- Prince Thun - in Flashback [Ch. 14]
- Stanley Price
- Lab Worker Turned to Clay [Ch. 1]
- Charles Sherlock
- Palace Televisor Operator
- Edwin Stanley
- Gen. Rankin [Chs. 1, 9]
- Tom Steele
- Martian Soldier
- Glenn Strange
- Ming's Soldier - in Flashback [Ch. 6]
- Ray Turner
- Zarkov's Servant [Ch. 1]
- Francis Walker
- Martian Soldier
- Bud Wolfe
- Martian Soldier-Pilot [Ch. 2]
