The bird has two very thick black eyebrow lines and light gray underparts, with whitish cheeks and throat, and a belly more or less washed with buff and cinnamon.

The female can be distinguished from the male by its duller eye features and its upperparts having less contrast between the crown, nape, and lower back.

The numbers of the species are difficult to assess and seem to have been overestimated, so in 2013 the International Union for Conservation of Nature changed its status from "vulnerable" to "endangered".

[10] In 2014, Éric Pasquet and colleagues published a phylogeny based on nuclear and mitochondrial DNA from 21 species of nuthatches.

[9] There is sexual dimorphism: the male has a deep black eye-stripe (faintly glossed blue) and off-white cheeks and throat, with the remainder of the underparts pale to light grey with a slight buff tinge on the centre of the belly and vent.

The juvenile resembles the females, but has the crown mealy, the upper parts are more gray than blue, and the eye features are duller.

[12] It has warm brown fringes on the tertials and greater coverts, and the flight feathers are fresh when those of an adult are worn out from moulting.

[12] Its large size makes the giant nuthatch quite distinctive, but in cases where this criterion is not obvious, there may be a risk of confusion with the chestnut-vented nuthatch (Sitta nagaensis), which however has reddish flanks, much smaller black eye-stripe, and does not have calotte and upper mantle lighter than the rest of the upper parts.

It usually flies straight over short distances, with whirring wingbeats, and its broad butterfly-like wings are visible as it drops from one branch to another.

[9][14] The study of stomach contents showed that the diet consisted of berries and arthropods, such as beetles, lepidoptera and ants.

It was located in a naturally occurring hole in the trunk of a tree, with the opening facing the sky, more than 2 m above the ground, and not bricked with mud as other nuthatches do.

[14] The giant nuthatch mainly appreciates pine forests, but can also be found in more open environments, foraging for food from one small tree to another.

In Thailand, it is found in the middle of oak and chestnut forests, among which mature large Benguet Pine are frequent on the ridge tops.

In Myanmar, it inhabits a large part of Shan State, and its distribution ends in the northwest at the Mogok Hills of the Mandalay region, in the central-west around Myinkyado, and in the south at Mount Nat Taung.

[14][17] It is probably present in the extreme northwest of Laos since it is found in neighboring Myanmar and Yunnan; in 2013, searches carried out in the habitats most likely to host the species would have been unsuccessful.

[16] It was reported in Doi Inthanon in the early 1980s, but it could be a confusion with the chestnut-vented nuthatch (S. nagaensis) since the large pine forests to which the species seems so related do not exist on this mountain.

[19] The species is present in many protected areas in China and Thailand, and a public awareness program was set up in Yunnan in 2007.

BirdLife International proposes further study of the exact distribution of the giant nuthatch, its numbers, and its habitat in order to better protect the species.