Well-preserved Early Jurassic radiolarians are obtained from a manganese band in the Nanjo Massif, Mino Terrane, central Japan. This paper is Part 1 of a serial descriptive work on an Early Jurassic radiolarian fauna from the Nanjo Massif and deals with nassellarians which possess a constricted or closed distal end. One new genus, Minocapsa, is erected, and 9 new species and 2 new subspecies are described : Tricolocapsa minoensis, T. (?) megaglobosa, T. (?) fera, Stichocapsa plicata plicata, S. plicata semiplicata, S. elegans, S. biconica, S. nanjoensis, Minocapsa cylindrica and M. globosa. The fauna from the Nanjo Massif is very similar to that of the upper Archicapsa pachyderma Zone of Jurassic radiolarian zones in Japan. The fauna is correlative with the lower Toarcian fauna in east-central Oregon, North America.