The South Block was in the background of extensional tectonics during the transition from Sinian(Ediacaran) to Cambrian, and the siliceous rocks developed widely in southest margin of Yangtze block. The deep water Sinian— Cambrian sections in central Hunan include the Doushantou Formation, Liuchapo Formation, composed mainly of bedded siliceous rocks with Si rich and C rich shale deposits, which is also overlain by the Niutitang Formation. Based on the analyses of major elements and rare earth elements, it was conclude that the Sinian— Cambrian siliceous rocks of central Hunan contain high contents of SiO2(generally over 92%) and have high Al/ (Al+Fe+Mn) value ( generally higher than 0.6). The shale PAAS normalized REE patterns for the Sinian—Cambrian siliceous rocks show weak to intermediate negative Ce anomalies and strong enrichment in HREEs relative to LREEs. Ce/Ce*, LaN/YbN and Y/Ho values for the siliceous rocks of Sinian Doushantuo Formation are 0.34~0.54, 0.05~0.10 and 38.00~51.44; the siliceous rocks from Sinian Liuchapo Formation and Cambrian Niutitang Formation have similar REE geochemical characteristics, Ce/Ce*, LaN/YbN and Y/Ho values for two groups of samples are 0.70~0.85, 0.06~0.37, 35.91~46.79 and 0.58~0.78, 0.26~0.40, 34.75~45.58 respectively. The characteristics of major and rare earth elements reflect that these siliceous rocks formed in the deep water basin far from continent and extensional faulting belts where terrestrial material and hydrothermal activities had no obvious effect on them. Although terrestrial input had an increasing tendency from Sinian to Cambrian, the origin of silica may derived from the thriving of the siliceous plankton. Sedimentary basin in central Hunan seemed like a passive continental margin basin during the transition from Sinian to Cambrian.