| Name | Source | Type | - |
| Aaamazzarite | Star Trek: The Motion Picture | Hairless humanoids that create objects biochemically from their mouths; also known as Therbians | - |
| Aalaag | Gordon R. Dickson's Way of the Pilgrim | Nine foot tall alabaster-skinned and white-haired humanoids with a biological instinct for racial-preservation instead of a human instinct for self-preservation, known as The Immaculate People in their language | - |
| Abh | Crest of the Stars | Genetically-enhanced humans | - |
| Abductors | Invader Zim, Squee | | - |
| Abu Chacha | Let's Shake It | Humanoid | - |
| 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 | Guyver: The Bioboosted Armor | | - |
| Aenar | Star Trek | Telepathic humanoid | - |
| Aeodronians | Battlelords of the 23rd Century | | - |
| Aerophibian | Ben 10 | Manta ray-like humanoids from the misty planet Aeropela, who can fly and swim at supersonic speeds, accelerate to speeds greater than light, and shoot neuroshock blasts from their eyes and tails to disable a victim's nervous system. | - |
| Affront | Iain M. Banks' Excession | | - |
| Agorian | Ratchet & Clank | | - |
| Akaali | Star Trek | | - |
| Akiss | Harry Turtledove's Worldwar series | Very large and dangerous reptilian animal in the mythology of the [The The Race (Worldwar)|Race (Worldwar)|Race]. It is comparable to Earth's mythical dragons. | - |
| Akrennians | Titan A.E. | Rat/hyena-like humanoids who apparently do not dream ; 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 | - |
| Alf | ALF | | - |
| The Alien | Satyajit Ray's The Alien and Banku Babu's Friend | | - |
| The Alien Girl | Thiagarajan Kumararaja's Super Deluxe | | - |
| Alien | The Hidden and its sequel | Parasitic and having the capability to possess its host | - |
| Alien Frogs | Taro the Space Alien | An alien species like frogs: James and his family | - |
| Alien Husbands | Adventure Time | This species of aliens is Gray, Tree Trunks' five alien husbands | - |
| Alien Mechawar | Taro the Space Alien | | - |
| 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 | - |
| Alzarians | Doctor Who | 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 aliens, they have non-poisonous scorpion tails as a formidable weapon. They lack mouths, so they use a technique called "thought-speak", similar to but not quite telepathy, and they have four eyes: two on their face, and two on stalks that give them 360 degree vision. They are the main enemies of the villainous Yeerks. | - |
| Andorians | Star Trek | Humanoid with blue skin, white hair, antennae | - |
| Andromeni | Battlelords of the 23rd Century | | - |
| Angara | Mass Effect: Andromeda | | - |
| Angol Mois | Sgt. Frog | | - |
| Angosian | Star Trek | | - |
| Annari | Star Trek | Humanoid | - |
| Anodite | Ben 10 | Free-spirited humanoid energy beings from the planet Anodyne, who can draw life from the mana around them. Old enough Anodites can use this manipulate reality, while even younger ones have a strong connection to magic. | - |
| 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 & Cocoon. | | - |
| Anticans | Star Trek | | - |
| The Anti-Monitor | DC Comics | | - |
| Appoplexian | Ben 10 | Muscular tiger-like humanoids from the planet Apploplexia. They value emotional openness, but this can be a problem since their primary emotion is rage, and they are proud fighters. Primarily, they use claws on their wrists that elongate when their rage increases, but are skilled in wrestling, though are fatally vulnerable to certain high pitched noises. | - |
| Aqualish | Star Wars | | - |
| Aquatoids | X-COM: Terror from the Deep | | - |
| Arachnichimp | Ben 10 | Four-eyed, four-armed monkey-like aliens from the jungle planet Arahnascimmia, they have the ability to produce strong webbing from their tails. | - |
| Arachnids | Battlelords of the 23rd Century | | - |
| Arachnoids | Serious Sam: The First Encounter | Scorpion-like | - |
| Aras | Perry Rhodan | | - |
| Arbryls | Ascendancy | | - |
| Arburian Pelarota | Ben 10 | Functionally extinct due to the destruction of their home planet Arburia, they are bulky yellow aliens that can curl into a ball, much like a pillbug, and are very hard to damage in ball form, and they use this to crush enemies either by bouncing around or rolling over them | - |
| 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. | - |
| Atraxi | Doctor who | | - |
| Atrocians | Ben 10 | Pathetic, short, stubby species that are invulnerable to all types of damage yet can feel what's hurting them. | - |
| 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 | | - |
| Azwaca | Harry Turtledove's Worldwar series | A large stock animal native to Home and used by the Race as food. They are also edible to humans. The Colonization Fleet brought azwaca and several other species of livestock to Tosev 3. As Earth plants were not equipped to deal with the extremely economic grazing patterns of these animals, some ecological damage resulted. This in turn led to diplomatic tensions between the Race and the various human powers that shared borders with Lizard-territory. | |
| Antispiral race | Gurren Laggan | | - |