The presence of idiomorphic plagioclase with oscillatory zonal structure serves to identify partially melted portion in high grade metamorphic rocks in the Hidaka Metamorphic Belt, Hokkaido. Pelitic and mafic anatexites are characterized by such a plagioclase accompanied by interstitial quartz-pool of sub-millimeter size. The melt-derived plagioclase develops in both the mesosome and leucosome of pelitic anatexites, and frequently ocurs in the quartz-pool of pelitic and mafic anatexites. The quartz-pools sometimes join together to make a veinlet in the anatexites. The chemistry of pelitic metamorphic rocks change with increasing metamorphic grade. Fe, Mg and Ca contents increase, and K content decreases with increasing metamorphic grade. LREE contents are nearly constant in the greenschist to amphibolite zones, but they are depleted in the granulite facies. Eu content increases with increasing metamorphic grade. Concludingly, pelitic granulites of zone E have a quite different chemistry from that of the lower grade pelitic gneisses. The bulk chemical compositions of pelitic anatexites with incipiently developed quartz-pools are very similar to those of the greenschist facies rocks. This chemical similarity is consistent with our observations that the anatexites melted in situ, but segregation of melts did not take place. A nebulitic pelitic anatexite is enriched in REE, as compared with pelitic gneisses, tonalites, granites and the other types of pelitic anatexites. The bulk partition coefficients between host amphibolites and their veins systematically change with the increasing of metamorphic grade, which suggests that the veins were segregated from their host amphibolites.