Abstract: During the recent regional geological surveying at a 1∶50 000 scale in Jingxin, Menglian, a radiolarian assemblage represented by Entactinia-Entactinosphaera including 6 species spaced in 4 genera has been obtained from the West Laba Formation in northwestern Menglian. This formation has been assigned to the Lower Permian in the 1:200 000 Menglian sheet. It is to be redetermined as the Middle Upper Devonian Manxin Formation on account of its rock association and sedimentary facies. This knowledge is of considerable geological significance in studying stratigraphy, tectonic setting, palaeogeography and structural activity in the surveyed area.