Hill believed there was one species of slender loris which was further split into six subspecies, two in India and four in Sri Lanka.

[3] In 1998 biological anthropologist Colin Groves recognised two species, L. tardigradus and L. lydekkerianus,[4] which have been widely accepted by the scientific community.

[5][9] A 2019 study based on partial CO1 sequences showed the taxon can be classified in a single haplogroup with L. t.

The gray slender loris has a wide variation in pelage colour and each subspecies can be identified by this.

The eyes are surrounded with darker fur and have orbits which look straight forward giving excellent stereoscopic vision and are located the closest together amongst the primates.

The hands are also highly specialised with a reduced second digit that allows the loris to cling to small branches.

[11] In Sri Lankan subspecies, Loris lydekkerianus grandis has short ears, and a heart-shaped face.

The behaviour of the gray slender loris is amongst the least known of the primates, despite the relatively large number of studies undertaking during the 2000s.

[13] In southern India, the nominate race is often found in acacia and tamarind dominated forests or scrubs near cultivations.

[11] It is found in south-western India roughly between the Tapti and Godavari Rivers down to the south coast of the subcontinent.

In south-western India, the Malabar gray slender loris occurs in the wet forests of the Western Ghats in the states of Karnataka, Kerala and Tamil Nadu up to an altitude of 1,200 metres (3,900 ft).

The Mysore gray slender loris inhabits the tropical dry forests of the Eastern Ghats in the states of Andhra Pradesh, Karnataka and Tamil Nadu, frequenting open Euphorbia scrub forests and Acacia trees at an altitude of 300–500 metres (980–1,640 ft).

[21] Although considered near threatened on the IUCN Red List and classified under Schedule I (Part 1) of the Indian Wildlife Act, 1972, the threat to these primates is increasing.