Five species of the genus Ecnomus McLachlan (Ecnomidae), including 2 new species, are recognized from Japan: E. hokkaidensis sp. nov. from Hokkaidu and E. sakishimensis sp. nov. from Ishigaki-jima and Iriomote-jima, Ryukyu Islands, are described. Ecnomus japonicus Fischer, originally described from Kyushu, is re-described. In addition, illustrations of the male and female genitalia are provided for E. tenellus (Rambur) and E. yamashironis Tsuda, which are common species in Japan. Ecnomus kososiensis Kobayashi, originally described from Honshu, and E. tsudai Kumanski, originally described from Korea, are synonymized under E. tenellus and E. japonicus, respectively.