[2] Alström's warbler often forages in a low, dense growth of forests.

The warbler tends to breed in bushes and small trees of low to moderate height, in recently cleared areas.

A molecular phylogenetic study published in 2018 found that neither Phylloscopus nor Seicercus were monophyletic.

[5] In the subsequent reorganization the two genera were merged into Phylloscopus which has priority under the rules of the International Commission on Zoological Nomenclature.

[7] The bird has a greyish-black color that fades on the forehead as well as a mix of green that surrounds the eyes.

[3] The underside of the bird is a vibrant yellowish-green color whereas the wings and back have a grey crown with black stripes.

[3] To distinguish this bird from others, the Alström's warbler is larger billed, smaller tailed, and has a more distinct white lining in the outer tail feathers than Martens's and Gray-crowned warblers.

[3] Its distribution in the non-breeding season is hard to estimate because there is an overlap of non-singing similar species which makes identification very difficult.