In this study,we carried out an REE geochemical study of lowermiddle Silurian organicrich bedded cherts and underlying Sinian volcanic rocks in the regions of northern Ruoergai (Zoigê) County in Sichuan and Diebu (Têwo) County in Gansu, central China. The aim of this study was to understand the origin of rare earth elements in hydrothermal cherts and factors affecting REE patterns, and establish a corresponding model. 28 samples of cherts from one drilling core and two profiles were studied using petrographic analysis, scanning electron microscopy (SEM) analysis, major and rare earth element analyses. 14 samples of volcanic rocks from one profile were investigated using major elements and REE analyses. Petrographic and SEM analyses of black hydrothermal cherts show that the black cherts have typical features of deposition structure and weak latestage metamorphism. The TAS diagram of lower Sinian volcanic rocks suggests that they are dominantly felsic volcanic rock, with minor being mafic volcanic rocks. Combined with previous results, comparison analysis of underlying Sinian volcanic rocks and overlying middleearly Silurian hydrothermal siliceous rock draw the following conclusions. (1) Tensional tectonic setting is an essential dynamic factor for formation of hydrothermal chert, REEs of which mainly derived from hydrothermal fluids, ancient seawater (mixed in continental matters). (2) Relative abundances of the REEs in hydrothermal cherts have a threshold, below which LREEs’ distribution pattern is consistent with that of hydrothermal fluids while HREEs’ distribution patterns consistent with that of underlying volcanic rocks; and above which LREEs’ distribution presents the characters of mixing of hydrothermal fluid with ancient water (terrestrial material). The LREE patterns of hydrothermal cherts are consistent with that of upper crust, while HREE patterns are consistent with that of underlying volcanic rocks. Therefore, hydrothermal chert deposited in a certain condition can indicate paleodepositional structure environment.