 Michael RennieKlaatu / Mr. Carpenter | Klaatu / Mr. Carpenter |
 Patricia NealHelen Benson | Helen Benson |
 Billy GrayBobby Benson | Bobby Benson |
 Sam JaffeProf. Jacob Barnhardt | Prof. Jacob Barnhardt |
 Hugh MarloweTom Stevens | Tom Stevens |
 Lock MartinGort | Gort |
 Freeman LuskGeneral Cutler | General Cutler |
 Edith EvansonMrs. Crockett | Mrs. Crockett |
 Frank ConroyMr. Harley | Mr. Harley |
 Frances BavierMrs. Barley | Mrs. Barley |
 John BrownGeorge Barley | George Barley |
 Olan SouleMr. Krull | Mr. Krull |
| MMarjorie CrosslandHilda | Hilda |
| EElmer DavisElmer Davis | Elmer Davis |
| HH.V. KaltenbornH. V. Kaltenborn | H. V. Kaltenborn |
| DDrew PearsonDrew Pearson | Drew Pearson |
| GGabriel HeatterGabriel Heatter (voice) | Gabriel Heatter (voice) |
 Harry LauterLieutenant in Charge of Landing Site | Lieutenant in Charge of Landing Site |
| JJames DoyleArmy Dr. White | Army Dr. White |
| LLarry DobkinBalding Army Doctor | Balding Army Doctor |
 Robert OsterlohArmy Examining Doctor | Army Examining Doctor |
| GGlenn HardyRadio Interviewer at Landing Site | Radio Interviewer at Landing Site |
 Tyler McVeyBrady | Brady |
 House Peters Jr.M.P. Captain at Barnhardt's | M.P. Captain at Barnhardt's |
 George LynnConference Colonel Ryder | Conference Colonel Ryder |
 Dorothy NeumannMargaret | Margaret |
 Wheaton ChambersMr. Bleeker | Mr. Bleeker |
 Carleton YoungZone Five Lieutenant Colonel | Zone Five Lieutenant Colonel |
 Harry HarveyThe Cab Driver | The Cab Driver |
| SSammy OggSammy | Sammy |
