The Solon Obo ophiolite belt in Inner Mongolia is located close to the border between China and Mongolia. It is an integral part of the Solon Obo tectonic suture formed by the closure of the Paleo-Asian Ocean between Siberia Craton and North China Craton in the Paleozoic. This ophiolite belt is a rare remnant of the Paleo-Asian Ocean and thus provides important samples for the study of tectonic evolution in the eastern part of the Central Asian Orogenic Belt in North China. The age of the tectonic event of the Solon Obo tectonic suture has been debated for a long time. Some researchers believe that it was from Silurian to Devonian whereas other researchers believe it was from Early Carboniferous to Early Permian. Here we report the first discovery of Early Permian radiolarians in the cherts of the ophiolite belt. The Solon Obo ophiolite belt is E-W trending, with a total length of ~100 km. It is mainly composed of ultramafic intrusive rocks such as harzburgite, lherzolite, dunite and pyroxenite, and gabbro, diabase, basalts and cherts. On the base of the field geological investigation and 1:10000 structure-lithology mapping in the Solon Obo area, we took cherts samples from the Solon Obo ophiolite belt in the Subuergen Hudag area of northern Urad Middle Banner, Inner Mongolia, and carried out studies including petrologic characteristics of cherts, separation and identification of the radiolarian fossils in cherts. Early Permian radiolarian fauna is first found in the chert of Solon obo ophiolite belt. This fauna is composed of 5 genera and 6 species (including 4 unidentified species and 1 new species), Pseudoalbaillella bulbosa , Ps. solonensis Wang sp. nov., Stigmosphaerostylus sp., Ruzhencevispongus sp., Cenosphaera sp., Latentifistula sp. etc. The new species, Pseudoalbaillella solonensis can be distinguished from Ps. u-forma by its holes in the end of the pseudoabdominal segment. Pseudoalbaillella bulbosa , found in Late Carboniferous-Early Permian cherty strata of Japan, Thailand, Chile, Western Coast of North America and South China is regarded as a zonal species of early Early Permian time in China and has become one mark of the boundary between Carboniferous and Permian cherty strata in open marine facies. This radiolarian fauna is characterized by rich Pseudoalbaillellids and Entactinids which have possessed about 45% of this fauna respectively. The Pseudoalbaillellids are mostly composed of the apical cones and many pseudothoraxes with smaller entire individuals. The Entactinids are numerous in number and their spines are longer, but incomplete due to break. Other radiolarians, such as Latentifistalids , Cenosphaerids and Ruzhencevispongids are rare. These radiolarian fossils possessing over 50% in whole rocks are considered as the radiolite which is a component of the ophiolite. Therefore, the time determined by radiolarian fossils may represent forming age of the ophiolites and this set of radiolite is known as a part of the Solon Obo ophiolite belt. The discovery of this radiolarian fauna has provided a key evidence about forming age of the Solon Obo ophiolite lasted until Early Permian. This new discovery, together with the previously reported zircon U-Pb ages of 279–296 Ma for the associated mafic-ultramafic rocks in the Solon Obo ophiolite belt, confirms that the final closure of the Paleo-Asian Ocean took place no early than Early Permian.