Sir Arthur Conan Doyle – Himself (appears in a frontispiece to the film)
Bessie Love – Paula White
Lewis Stone – Sir John Roxton
Lloyd Hughes – Edward Malone
Wallace Beery – Professor Challenger
Arthur Hoyt – Professor Summerlee
Alma Bennett – Gladys Hungerford
Virginia Browne Faire – Marquette the half-cast girl (uncredited)
Bull Montana – Ape Man/Gomez