Anisomeridium japonicum H. Harada sp. nov. is described as new from Chiba-ken, central Japan. It is characterized by having greenish gray thin thallus, small perithecia (0.15- 0.2 mm diam.), and 1-septate, relatively small ascospores (9-16 X4-6/im), and by growing on non-calcareous rocks in semi-freshwater habitats. lichens, lichenized Ascomycota, Monoblastiaceae, Anisomeridium, taxonomy, new species, Japan