The species of the genus Isonychia Eaton, 1871 (Isonychiidae) of East Palaearctic are revised. Two subgenera, Isonychia s.s. and Prionoides Kondratieff et Voshell, 1983, are represented in the Palaearctic. New species and subspecies of Isonychia s.s. are described: I. sexpetala sp. nov., I. ussurica sibirica subsp. nov., I. concoloria sp. nov., I. crassiuscula sp. nov., and I. vshivkovae sp. nov. with subspecies I. vshivkovae vshivkovae and I. vshivkovae sinitshenkovae subsp. nov. A new species group japonica, with three species (I. crassiuscula, I. vshivkovae, and I. japonica), is recognized on the basis of adult and larval characteristics. The name Isonychia hainanensis She et You, 1988 is synonymized with Isonychia ignota (Walker, 1853) syn. nov.