Three specimens of the predatory salifid leech Mimobdella japonica Blanchard, 1897 were collected from Hachijojima island, Izu Islands, Japan. This species was previously known only from Okinawajima and Amamioshima islands in the Ryukyu Islands, Japan; this is the first record of this species from the Izu Islands. A morphological description based on these specimens is presented here. In addition, we evaluated the genetic diversity of this species based on sequences of cytochrome c oxidase subunit I, tRNACys, tRNAMet, 12S rRNA, tRNAVal, 16S rRNA, tRNALeu, and NADH dehydrogenase subunit 1 obtained from specimens of M. japonica collected recently from all three islands. The only difference noted among them was a unique ND1 sequence detected from two specimens collected on Okinawajima. The possibility of human-mediated introduction of M. japonica to one or more of these islands is discussed.