Invertebrate fauna of Khosrov Reserve comprises over 1500 species, including 1427 species of insects, 62 molluscs and 3 scorpions. Insects represent 10 orders: Odonata, Mantoptera, Phasmoptera, Orthoptera, Dermoptera, Homoptera, Coleoptera, Lepidoptera, Diptera and Himenoptera.
Vertebrate fauna numbers 283 species.
According to the earlier faunistic revisions dated 1950s and 1980s, mammalian fauna of Khosrov Reserve numbers 41 species. However, with exclusion of the Urts Ridge from this protected area it becomes unclear whether the 12 mammals living in its semi-deserts can be considered as representatives of the reserve fauna. This dozen of species includes the long-eared hedgehog (Hemiechinus auritus), Mehely's horseshoe bat (Rhinolophus mehelyi), lesser horseshoe bat (Rhinolophus hipposideros), greater horseshoe bat (Rhinolophus ferrumequinum), Ognev's bat (Vespertilio ognevi), mid-day jird (Meriones meridianus), Vinogradov's jird (Meriones vinogradovi), Tristram's jird (Meriones tristrami blackleri), small five-toed jerboa (Allactaga elater), Williams's jerboa (Allactaga williamsi), social vole (Microtus socialis) and Asiatic wild cat (Felis silvestris ornata). It is possible, however, that at least some of them have survived in the semi-desert habitat of the Mt. Eranos in the Garni district. The Armenian mouflon (Ovis orientalis gmelinii) inhabits the Urts Ridge, but is absent in Khosrov Reserve.
Common representatives of mammalian fauna are the wild boar (Sus scrofa), gray wolf (Canis lupus), brown bear (Ursus arctos), Eurasian lynx (Lynx lynx), red fox (Vulpes vulpes), badger (Meles meles), European hare (Lepus europaeus), least weasel (Mustela nivalis) and stone marten (Martes foina). Recently, the first records of the Indian porcupine (Hystrix indica) were documented.
Bird fauna includes 192 species from 44 families what makes 56% of Armenia's ornithofauna. Of them, 63 species are resident, 83 nesting, 83 occuring during migrations, 11 wintering, 10 vagabond and 5 casual. Diversity of raptors is particularly fascinating, being represented by the bearded vulture or lammergeier (Gypaetus barbatus), Egyptian vulture (Neophron percnopterus), Eurasian griffon vulture (Gyps fulvus), peregrine (Falco peregrinus), lanner (Falco biarmicus) and many others. Gallinaceous birds are four: the Caspian snowcock (Tetraogallus caspius), chukar (Alectoris chukar), grey partridge (Perdix perdix) and common quail (Coturnix coturnix). Semi-desert foothills are inhabited by the European nightjar (Caprimulgus europaeus), European bee-eater (Merops apiaster) and others. Passerines are very abundant and widespread.
Reptiles of Khosrov Reserve number 33 species which inhabit all landscapes from semi-deserts up to subalpine meadows. The common lizards are the Caucasian agama (Laudakia caucasia), Azerbaijani lizard (Darevskia raddei), Nairi lizard (Darevskia nairensis), snake-eyed lizard (Ophisops elegans), Caucasus emerald lizard (Lacerta strigata), European glass snake (Pseudopus apodus) and others. Among the snakes, the wood snakes (Coluber ravengieri, C. nummifer), mountain grassland viper (Vipera eriwanensis), levantine viper (Vipera lebetina) and others can be mentioned.
Khosrov Reserve is inhabited by only 5 species of amphibians: the Eurasian marsh frog (Rana ridibunda), green toad (Bufo viridis), long-legged wood frog (Rana macrocnemis), tree frog (Hyla savignyi) and Syrian spadefoot (Pelobates syriacus).
Fish species are nine: the brook trout (Salmo trutta fario), Transcaucasian barb (Capoeta capoeta), Kura barbel (Barbus lacerta cyri), Kura bleak (Alburnus filippi), North Caucasian bleak (Alburnus alburnus hohenackeri), spirlin (Alburnoides bipunctatus), golden spined loach (Sabanejewia aurata), Nemacheilus angorae and Barbatula barbatula caucasica.