Abstract: Mesoproterozoic sedimentary records in the Hainan Island are significant for discussing the continental crust evolution of the South China Massif.In our studies, the formation age of metamorphic conglomerate in the sandstone-slate combination of the Ordovician Gangoucun Formation in the Sanlangling area of the Sanya city, Hainan Island, were redetermined.Total 65 detrital zircons from the conglomerate were measured for U-Pb dating.The U-Pb ages of the zircons range from 2691 Ma to 1350 Ma, and are clustered at 2691~2444 Ma, 1838~1632 Ma, and 1540~1350 Ma, with two main peaks at ~1699 Ma and ~1440 Ma and a subordinary peak at ~2461 Ma.Based on the youngest detrital zircon age of ~1350 Ma for the conglomerate, without 1250~1100 Ma and 1000~900 Ma age records which are common in the Hainan Island, it is suggested that the metamorphic conglomerate was deposited at 1350~1250 Ma.This is the first time that a Mesoproterozoic conglomerate formation has been recognized on Hainan Island, rather than the Ordovician sedimentary rocks previously classified.The metamorphic conglomerates have high compositional maturity and middle texture maturity, which are consistent with the sedimentary features of high-density debris flow in the rift basin.They might represent the sedimentary response to the final breakup of the Columbia supercontinent in the Hainan Island.