The significance of the sanctuary lies in its ecological, faunal, floral and geomorphological importance. Various factors contributing to the significance of the area are as indicated below:
Abundance of Gluta travancorica, an endemic species of Agasthyamalai region.
It is a treasure house of plant diversity. About 1257 species of flowering plants belonging to more than 150 families are reported from this sanctuary of which 309 species are endemic to Western Ghats.
Occurrence of more than 100 species of threatened plants within the sanctuary, which is the type locality of several endemic and threatened species.
Presence of wild populations of lion-tailed macaque, a highly endangered species.
Presence of other wild animals like elephant, tiger, leopard, bear, Nilgiri langur, Malabar giant squirrel etc.
High degrees in diversity of avifaunal wealth – 267 species of birds were reported including migratory, endemic and endangered species.
An artificial lake of nearly 18.69Sq.km within the sanctuary attracts a large number of water birds
The watershed of Kallada reservoir roughly coinciding with the boundary of the sanctuary is an important source of water for irrigation purposes to the districts of Kollam and Pathanamthitta.
As part of the Agasthyamalai Biosphere Reserve, the sanctuary has an important role to play in conserving the rich biological diversity.
Presence of unique vegetation of Myristica swamps.
The first eco-tourism project in India, Thenmala Eco-tourism Project making use of land and water area of the sanctuary add colour to the prominence of the sanctuary, its role in the nature education and promoting ecologically sustainable tourism.