The pupal cremasters of twelve species of Japanese oak-feeding Phyllonorycter are examined. The cremasters, even those of closely related species, are specifically distinct. Combined with descriptions of European and North American species, the present results indicate that the cremaster can be used as a diagnostic character for the species of Phyllonorycter. A new species, P. persimilis, which was previously confused with P. similis Kumata, and the female of P. nipponicella (Issiki), hitherto unknown, are described. The nipponicella complex including these species is reviewed and the speciation of its members is discussed in relation to diversification of the host plant preference.