List of fictional alien species: A
| Name | Source | Type |
|---|---|---|
| Aaamazzarite | Star Trek | Hairless humanoids that create objects biochemically from their mouths |
| Aalaag | Gordon R. Dickson's Way of the Pilgrim | |
| Abh | Crest of the Stars | Genetically-enhanced humans |
| Abductors | Invader Zim, Squee | |
| Abzorbalof | Doctor Who | Human-absorbing humanoid |
| Abyormenites | Hal Clement's Cycle of Fire | floating balloons |
| Acamarian | Star Trek | |
| Acquarans | Farscape | Humanoid |
| Adipose | Doctor Who | Tiny, round humanoids made of fat |
| Advent | Sins of a Solar Empire | Humanoid |
| Advents (aka Uranus or the Creators) | Guyver: The Bioboosted Armor | |
| Aenar | Star Trek | Telepathic humanoid |
| Aeodronians | Battlelords of the 23rd Century | |
| Affront | Iain M. Banks' Excession | |
| Agorian | Ratchet & Clank | |
| Akaali | Star Trek | |
| Akrennians | Titan A.E. | Rat/hyena-like humanoids who apparently do not dream (or bathe much); the character Preed is an Akrennian. The food "Akrennian Beetle Sushimi" is also featured in the film, hinting that insect-like life-forms are also found on their home planet. |
| Akritirians | Star Trek | |
| Albategna | The webcomic Not So Distant | Large black-and-white creatures with six tentacular limbs (two for walking and four for manipulating) |
| The Alien | Satyajit Ray's The Alien and Banku Babu's Friend | |
| Alien | The Hidden and its sequel | Parasitic and having the capability to possess its host |
| Alien Sex Goddesses | Church of the SubGenius | |
| Alkari | Master of Orion | |
| Allasomorph | Star Trek | |
| Amaut | C. J. Cherryh's Alliance-Union universe | |
| Altarians | Galactic Civilizations | Humanoid |
| Amazonians | Futurama | Giant humanoid women. Men of this species have died out. |
| Amnioni | Stephen Donaldson's The Gap Cycle | Humanoid |
| Amorphs | Schlock Mercenary | |
| Anabis | The Voyage of the Space Beagle by A. E. van Vogt | |
| Ancients | Farscape | |
| Ancients | Freespace | Technologically advanced beings that were wiped out several thousand years ago. Unknown physical description. |
| Ancient | Stargate SG-1 | Humans from Earth, with a developed intelligence, who in the age of the creation of the pyramids, left Earth for universe exploration. |
| Andalites | K. A. Applegate's Animorphs | Centaur-like, with non-poisonous scorpion tails, and blue fur |
| Andorians | Star Trek | Humanoid with blue skin, white hair, antennae |
| Andromeni | Battlelords of the 23rd Century | |
| Angol Mois | Sgt. Frog | |
| Angosians | Star Trek | |
| Anodite | Ben 10 Alien Force | |
| Antarans | Master of Orion II | Marauders exiled to a pocket dimension |
| Antarians | Imperium Galactica II: Alliances | |
| Antedeans | Star Trek | |
| Anterians | The Suite Life on Deck | |
| Anticans | Star Trek | |
| The Anti-Monitor | DC Comics | |
| Aqualish | Star Wars | |
| Aquatoids | X-COM: Terror from the Deep | |
| Arachnids | Battlelords of the 23rd Century | |
| Arachnoids | Serious Sam: The First Encounter | Scorpion-like |
| Aras | Perry Rhodan | |
| Arbryls | Ascendancy | |
| Arburian Pelarota | Ben 10 | |
| Arcadians | Star Trek | |
| Arceans | Galactic Civilizations | |
| Arcturians | Star Trek | |
| Argolin | Doctor Who | Humanoid |
| Arilou Lalee'lay | Star Control | Humanoid - 'Grey' alien |
| Arisians and Eddorians | E. E. Smith's Lensman novels | |
| Ark Megaforms | Noon Universe | |
| Arkonides | Perry Rhodan | |
| Armada of Annihilation | Axelay | |
| Arquillians | Men in Black | |
| Airlia | Area 51 novel series by Robert Doherty | Humanoid, see moai |
| Arnor | Galactic Civilizations II: Dread Lords | |
| Asari | Mass Effect | Blue-skinned feminine humanoids |
| Aschen | Stargate SG-1 | Humanoid |
| Asgard | Stargate SG-1 | Grey humanoid |
| Aslan | Traveller RPG | Feline humanoid |
| Asuran | Stargate Atlantis | |
| Atavus | Earth: Final Conflict | Humanoid |
| Atevi | C. J. Cherryh's Foreigner series | Tall, dark, mysterious humanoids. Culture progresses rapidly from steam-age to contemporary and beyond perhaps due to their numerological language. Assassin's Guild rather than police. |
| Aurelians | Advent Rising | |
| Autobot | Transformers | A machine race that can transform between a humanoid form and that of a certain machine, depending on the specific Autobot |
| Auronar | Blake's 7 | |
| Autons | Doctor Who | Living plastic beings |
| Axanars | Star Trek | |
| Axons | Doctor Who | |
| Azathoth | Cthulhu Mythos | |
| Azgonians | Perry Rhodan | |
| Aziam | Battlelords of the 23rd Century |