ummary Radiolarians are found in the cherts of the Xingshuwa Ophiolite Belt on the northern side of Xar Moron River, Nei Monggol, comprising 14 species (including 1 conformis and 4 unnamed species) representing 11 genera, together with a plate like conodont Mesogondonella sp. These fossils are commonly discovered in the Middle Permian (Guadalupian) strata of Southwest Japan, Oregon and Nevada of western North America, the Philippines, Southeast Thailand, Guangxi and western Yunnan of China, and are regarded as some important members in the Follicucullus scholasticus Fo. ventricosus Zone, the Fo. bipartitus Fo. charveti Zone or the Neoalbaillella optima Neo. ornithoformis Zone. This fauna is interpreted as middle and late Guadalupian in age which also may be the forming time of the Ophiolite Belt and the final closing time of the Mongolian ocean to form the collisional suture between the Sino Korean and the Siberian plates. We consider this Ophiolite Belt as the Product of the Hercynian plate tectonic movement, the Xar Moron River Fault as the collisional suture between the Sino Korean and the Siberian plates; and the northern Ophiolite Belt of this River as the southern marginal orogen of the Siberian plate, instead of part of the northern marginal orogen of the Sino Korean plate.