 | Michael Rennie als Lord John Roxton |
 | Jill St. John als Jennifer Holmes |
 | David Hedison als Ed Malone |
 | Claude Rains als Prof. George Edward Challenger |
 | Fernando Lamas als Manuel Gomez |
 | Richard Haydn als Prof. Summerlee |
 | Ray Stricklyn als David Holmes |
 | Jay Novello als Costa |
 | Vitina Marcus als Native Girl |
 | Ian Wolfe als Burton White |
| Colin Campbell als Prof. Waldron (uncredited) |
| John Graham als Stuart Holmes (uncredited) |
 | Larry Chance als Indian Chief (uncredited) |
| Bert Stevens als Reporter at Airport (uncredited) |
 | Al Bain als Man at Airport (uncredited) |
 | Bess Flowers als Guest at Zoological Institute Forum (uncredited) |
 | Kenner G. Kemp als Guest at Zoological Institute Forum (uncredited) |
| Cosmo Sardo als Guest at Zoological Institute Forum (uncredited) |
| Murray Pollack als Guest at Zoological Institute Forum (uncredited) |
| Willis H. O'Brien | Visual Effects |
| Charles Bennett | Screenplay |
| Paul Sawtell | Original Music Composer |
| Bert Shefter | Original Music Composer |
| Irwin Allen | Screenplay |
| Irwin Allen | Director |
| Irwin Allen | Producer |
| Paul Zastupnevich | Costume Design |
| Walter M. Scott | Set Decoration |
| Hugh S. Fowler | Editor |
| Winton C. Hoch | Director of Photography |
| John Sturtevant | Set Decoration |
| Arthur Conan Doyle | Novel |
| Ben Nye | Makeup Artist |
| Helen Turpin | Hairstylist |
| Duncan Cramer | Art Direction |
| Walter M. Simonds | Art Direction |
| Joseph Kish | Set Decoration |
| Ad Schaumer | Assistant Director |
