List of fictional alien species: J
| Name | Source | Type |
|---|---|---|
| Jaffa | Stargate SG-1 | Genetically altered humans with pouches that are designed to incubate Goa'uld larvae. |
| Jaridians | Earth: Final Conflict | Humanoid |
| James (Frog) | Taro the Space Alien | An alien frog |
| Jawa | Star Wars | Creatures that live in the Tatooine desert. Their appearance is known to few as they often have robes covering the whole of their bodies. |
| Jem'Hadar | Star Trek | |
| Jenova | Final Fantasy VII | |
| Jezzedaic Priests | Battlelords of the 23rd Century | |
| Ji Rousang | Legend of Heavenly Tear: Phoenix Warriors | Humanoid |
| Jile | Let's Shake It | Humanoid |
| Jiralhanae | Halo | Known more commonly as Brutes. Part of Covenant Hierarchy. |
| Jjaro | Marathon Trilogy | |
| J'naii | Star Trek | |
| Jocaceans | Farscape | Humanoid |
| Jophur | David Brin's Uplift Universe | |
| Jorenians | S.L. Viehl's StarDoc series and associated universe | Large blue-skinned humanoid with retractile claws. |
| Jotoki | Larry Niven's Known Space | |
| Joozian | South Park | Their skin is dull yellow, with light brown markings and have beady eyes. Only male Joozians have been shown. |
| Judoon | Doctor Who | Rhino-like Humanoid |
| Junk squids | Void Bastards | Giant squid-like non-sapient omnivorous species capable of surviving in hard vacuum and large enough to devour even sizeable spacecraft. |