The Xiuning Formation (formerly known as the Zhitang Formation) developed in Jiande area, northwestern Zhejiang Province, is one of the most important Neoproterozoic stratigraphic units in South China block. However, its depositional age and regional correlation have been debated for a long time. Our LA- ICP- MS zircon U- Pb dating results show that tuff samples from Lower and Upper part of the Xiuning Formation produce U- Pb ages of 785.0±2.8 Ma (MSWD=0.85，n=37) and 727.5±7.3 Ma (MSWD=0. 64，n=7), respectively. A synthesis of available data suggests that the sedimentary time interval of the Xiuning Formation spans ca. 70 Ma from ~800 Ma to ~728 Ma. Field observations show that shallow water sedimentary structures occur abundantly in the Xiuning Formation, suggesting a dominant alluvial fan and offshore to shallow sea (lake) rather than glacial depositional environment. Regionally, the depositional period of Xiuning Formation is synchronous with the Banxi Group, Liantuo Formation, Suxiong Formation (Kaijianqiao Formation), and Chengjiang Formation but predates the glaciogenic Chang’an Formation. It should be defined as a set of rifting filling sequences overlying the unconformities of the Sibao Orogeny and underlying the Nanhua glaciogenic strata in South China.