It was recently split from the yellow-browed warbler (Phylloscopus inornatus), based on differences in morphology, bioacoustics, and molecular characters. The Western Hume's leaf warbler's range overlaps with that of the yellow-browed warbler in the western Sayan Mountains, but the species apparently do not hybridize. The divergence between the two species has been tentatively estimated at roughly 2.5 million years ago (mya), and that between P. h. humei and P. h. mandelli at about 1 mya.