From the little winged Travancore Evening Brown, a rare butterfly, to the majestic Indian elephant to the tiger, the Periyar forests support numerous faunal varieties. The sanctuary has recorded 62 species of mammals. A boat ride on the scenic lake inside the sanctuary is an attractive option to watch the animals, including elephant herds bathing and playing in the water.
According to a 2010 estimate, there are 53 tigers in the reserve. The Tiger population is not confined to the sanctuary. Instead, it lies contiguous with the bordering forests which fall in Kerala and the nearby state of Tamil Nadu.
The sanctuary has a fairly good presence of elephants numbering between 900 and 1000. Other important inhabitants are the Sambar, Barking Deer, Mouse Deer, Gaur, Indian Wild Dogs, Leopards, Foxes and Mongoose. The primates include lion-tailed macaque, bonnet macaque, Nilgiri Langur and Langur.
45 species of reptiles, 27 species of amphibians and 38 species of fish have also been reported in the sanctuary.