Abstract: Ordovician strata in central- southern Hunan consist of"finer clastic-chert- bearing series-coarser clastic rock", and their thickness varies regularly. Spatially, the thickness contours are distributed northeastwards nd meanwhile, the thickest tends to move southeastwards. In the study area, chert samples of Yanxi Formation in Lingkou section show high SiO₂ values (89.08 %- 94.32%) and Al/(Al+Fe+Mn) ratios (0.52-0.79), and are characterized by slight enrichment of LREE and no obvious cerium and europium anomalies. Samples of equivalent formation in Daqiao section shows high SiO₂ values (91.74 %-95.14%), and the Al/(Al+ Fe+Mn) ratios range from 0.34 to 0.56, with characteristics of LREE enrichment, intermittently negative cerium anomaly and no europium anomaly, and low Y/Ho ratios (20.65±1.63). Geochemical characteristics and discrimination diagrams of middle-upper Ordovician cherts in central-southern Hunan indicate that these rocks were bio-genetic and formed in an open continental margin. A correlation with equivalent formation in adjacent areas shows that these cherts have similar origins and sedimentary environments, which indicates that they formed in the same basin. Combined with the analysis of the iso-thickness diagram, it could be suggested that the basin in central-southern Hunan experienced the change from passive margin to foreland basin during Ordovician, and the cherts probably resulted from this transition. In addition, there is no obvious hydrothermal activity, suggesting the geodynamics that caused the uplift of Cathaysian block might have been located to the further southern or southeastern extension range of the cherts series in central-southern Hunan.