<p>Jurassic accretionary complex of the Ashio belt is exposed in the Ashio Mountains, central Japan. Lithology, stratigraphy, fossil age and geologic structure are summarized in this article, on the basis of the geological survey of the Kiryu and Ashikaga District (Quadrangle series 1:50,000) and previous studies in adjacent districts. The Jurassic accretionary complex in the Ashio Mountains comprises four tectonostratigraphic units, namely the Kurohone–Kiryu, Omama, Kuzu and Gyodosan (newly named) complexes. The Kurohone–Kiryu Complex presents broken to coherent facies and is composed mainly of mudstone and chert and moderate amounts of siliceous claystone, with small amounts of basaltic rocks, carbonate rocks, siliceous mudstone, sandstone and pelitic mixed rock. This complex is characterized by dominant of pelitic rock that cleavage develops. This complex is subdivided into the Upper and Lower parts. The Omama Complex presents broken to mélange facies, and consists mainly of basaltic rocks, chert and mudstone, with small amounts of carbonate rocks, siliceous mudstone, sandstone and pelitic mixed rock. This complex is subdivided into the Upper and Lower parts, and the pelitic mixed rock are dominant in the Upper part. The Kuzu Complex is subdivided into three units (Units 1, 2 and 3). Units 1 and 3 are characterized by coherent facies of chert–clastic sequence comprising chert, siliceous mudstone, mudstone, alternations of sandstone and mudstone and sandstone, in ascending order. Unit 2 comprises basaltic rocks and carbonate rocks with conglomerate, siliceous mudstone and mudstone. The Gyodosan Complex presents mélange facies and is composed mainly of pelitic mixed rock and chert, with siliceous mudstone, mudstone and sandstone. Three faults as complex boundaries were recognized: the Kiryugawa Fault (between the Kurohone–Kiryu and Omama complexes), Kanma Fault (newly named: between the Kurohone–Kiryu and Kuzu complexes) and Oiwa Fault (newly named: between the Kuzu and Gyodosan complexes). Geologic structure of the Jurassic accretionary complex is characterized by several folds (e.g. Umeda Syncline, Hikoma Anticline, Kuzu Syncline) having NE–SW axial trace. On the basis of radiolarian fossils from pelitic rock of each complex, the accretionary age of the Omama and Gyodosan is after the middle Middle Jurassic, and that of the Kurohone–Kiryu Complex and Unit 2 of the Kuzu Complex is after the late Middle Jurassic. The accretionary age of units 1 and 3 of the Kuzu Complex is after the early Late Jurassic. Based on the comparison with tectonostratigraphic units of the Mino belt, the Kurohone–Kiryu Complex can be correlated to the Nabi and Shimashima complexes; the Omama Complex is correlated to the Funafuseyama and Shirahone complexes; the Kuzu Complex is correlated to the Kamiaso and Sawando complexes. The Gyodosan Complex resembles the Kuze Complex in including Permian chert: however, the Kuze Complex includes basaltic rocks and carbonate rocks whereas the Gyodosan Complex lacks these rocks.</p>