Reptiles
45 species constitute the reptilian diversity. These include 30 species of snakes, 13 species of lizards and two species of turtles. Among the snakes, all the four deadly venomous species found in Kerala such as King cobra, Cobra, Russels viper and Krait were recorded from Periyar. The king cobra, an endangered rainforest species is frequently sighted near Sabarimala in the Reserve. Malabar pit viper, Hump nosed pit viper, Striped coral snake etc. are some of the other snakes found. Of the 13 species of lizards 4 are endemic to Western Ghats. Monitor lizard is commonly seen. Flying lizard, Forest dwarf gecko and the Green calotes are some of the other fairly distributed reptiles.

Amphibians
Amphibians are among the least studied vertebrate groups in Periyar. A total of 27 species have been recorded and of these, 10 are endemic to Western Ghats. Micrixalus fuscus, Micrixalus nudis, Rana malabarica, Rana beddomei, Rana curtipes, Rana brevipalmata, Rana temporalis, Philatus beddommii and Racophorus malabaricus are the Western ghat endemic species found in Periyar.

Fishes
A total of 38 species of fishes are listed. Of these, 4 species are endemic to this Reserve. They are Periyar trout (Lepidopygopsis typus), Periyar lattia (Crossocheilus periyarensis) Periyar barb (Puntius micropogon periyarensis) and Noemacheilus menoni. Periyar is an important abode of the well known game fish, mahseer Tor khudree, a western ghat endemic species. Channa barb, Curcuma barb, and Travancore loach are the other Western Ghat endemic species found here. Tilapia and Common European carp are the two introduced species now distributed abundantly in the lake.

Invertebrates
Very few surveys and other taxonomic studies have been carried out for invertebrates. The predominant invertebrate orders found in Periyar are protozoans, annelids, arthropods and molluscans.