Abstract Parasitoid complexes of four microlepidopteran leaf‐mining genera, Phyllonorycter, Caloptilia (Gracillariidae), Tischeria (Tischeriidae) and Stigmella (Nepticulidae), which make mines on two oaks, Quercus dentata and Quercus mongolica , were studied at the Ishikari Coast, Hokkaido, northern Japan. In total, twenty‐five parasitoid species were recognized. Phyllonorycter showed the highest parasitoid‐species richness among the four leaf‐mining genera. The number of parasitoid species associated with leaf miners on Q. dentata was nearly equal to that associated with miners on Q. mongolica , but a considerable difference was observed in the faunal make‐up of parasitoids between leaf miners on the two oaks. The dominant parasitoid species differed between Phyllonorycter leucocorona and Phyllonorycter similis even on the same oak, Q. dentata . Factors influencing the host ranges of parasitoids and the parasitoid richness of host species or genera are discussed on the basis of the koinoparasitism/idioparasitism categorization.