The genus Isonychia Eaton, 1871 is widely distributed across the Holarctic and Oriental regions. However, no representatives of this genus have been reported from southwestern China, a region known for its high biodiversity. Here, we described and illustrated Isonychia latiassp. nov., a new species recently collected from Guizhou Province, southwestern China, across all developmental stages. The imagos of this new species exhibit some uncommon characters within Isonychia, such as brown mid- and hindlegs, and pale stripes on the thorax. To explore the phylogenetic status of this new species within Isonychia, a multigene phylogenetic analysis was conducted.