In recent years, the development of genetic diagnosis technology has revealed that Anisakis type I larvae is composed of not one, but several sibling species, of which at least five have been identified (A. simplex sensu stricto, A. pegreffii, A. simplex C, A. ziphidarum, and A. typica). However, the distribution of these sibling species is not well known. In the present study, we identified the Anisakis type I larvae obtained from a patient diagnosed with anisakiasis as A. simplex sensu stricto, by PCR-RFLP on the ITS region, including the 5.8 small subunit rRNA gene. Furthermore, by using the PCR-RFLP method on Anisakis type I larvae obtained from Japan (East China Sea) and the South China Sea, we were able to identify 4 sibling species; A. simplex sensu stricto, A. pegreffii, a hybrid genotype, and A. typical-like larvae. We analyzed the ITS sequence of A. typical-like larvae, because the PCR-RFLP result was slightly different from D' Amelio et al. (2000) and was able to confirm the identification.