- Buster Crabbe
- Flash Gordon
- Carol Hughes
- Dale Arden
- Charles Middleton
- Emperor Ming
- Anne Gwynne
- Sonja [Chs. 2, 6-12]
- Frank Shannon
- Dr. Alexis Zarkov
- John Hamilton
- Prof. Gordon [Chs. 1, 4]
- Herbert Rawlinson
- Dr. Frohmann [Chs. 1, 4]
- Tom Chatterton
- Prof. Arden [Chs. 1, 4]
- Shirley Deane
- Princess Aura
- Lee Powell
- Capt. Roka
- Roland Drew
- Prince Barin
- Don Rowan
- Capt. Torch
- Victor Zimmerman
- Lt. Thong
- Edgar Edwards
- Capt. Turan
- Ben Taggart
- Gen. . Lupi [Chs. 1-2]
- Michael Mark
- Prof. Karm [Chs. 5-10]
- Earl Dwire
- Janda [Ch. 1]
- Harry C. Bradley
- Keedish [Chs. 6-7]
- Sigurd Nilssen
- Count Korro [Chs. 1-2]
- Mimi Taylor
- Verna [Ch. 5]
- Byron Foulger
- Prof. Drok [Chs. 11-12]
- William Royle
- Capt. Sudan [Chs. 1-9]
- Ernie Adams
- Minor Role
- Roy Barcroft
- Ming's Soldier [Ch 6, 10-12] / Arborian Sentry [Ch 6] (uncredited)
- Robert Blair
- Minor Role
- Jean Brooks
- Olga - Ming's Henchwoman [Ch. 5]
- Allan Cavan
- Man with Thinking Brain [Ch. 1]
- Wheaton Chambers
- Scientist [Chs. 1, 4]
- Lane Chandler
- Ming's Soldier [Chs. 3-5, 7-8, 12]
- Donald Curtis
- Ronal [Chs. 1-12]
- Carmen D'Antonio
- Ming's Dancing Girl [Chs. 1, 3-4]
- Harold Daniels
- Minor Role
- Luli Deste
- Queen Fria [Chs. 1-2]
- Paul Douglas
- Guard
- John Elliott
- Scientist
- Jack Gardner
- Prof. Gordon's Radio Operator [Chs. 1, 4]
- Jack George
- Scientist [Chs. 1, 4]
- Pat Gleason
- Minor Role
- Saul A. Goodkind
- Various Characters
- Reed Howes
- Barin's Ship #5 Commander
- Bill Hunter
- Guard
- Mala
- Prince of the Rock People [Chs. 7-9]
- Vivian Mason
- Ming's Gong Girl [Chs. 1-4]
- Eddie Parker
- Arborian Prison Guard [Ch. 10]
- Ernie Payson
- Minor Role
- Joey Ray
- Prof. Gordon's Assistant [Ch. 1]
- Paul Reed
- Minor Role
- Gene Rizzi
- Ming's Soldier
- Jack Roper
- Man of Low Intellect [Ch. 1]
- Charles Sherlock
- Kroad - Guard [Ch. 11]
- Clarice Sherry
- Queen Grenda
- Tom Steele
- Ming's Pilot [Ch. 11]
- Charles Waldron Jr.
- Minor Role
- Chief Yowlachie
- King of the Rock People [Chs. 7-9]
