Abstract: In order to obtain the collision time of the Qiongnan block and the Qiongzhong block,or the forming time of the Qiongnan Suture Zone in the northern South China Sea,the authors collected the samples of garnet quartz schist and granitic gneiss for LA-ICP-MS zircon U-Pb dating. The results show that the protolith of garnet quartz schist is a kind of sedimentary rock formed after late Devonian; three concordant/near concordant data from the shells of metamorphic zircons indicate the collision time of about (233±4) Ma; and the protolith of the granitic gneiss is granite that formed when tectonic emplacement happened about (242±5) Ma, and the dating results of (206±3) Ma of eight zircon shells suggest the time of anatexis of granitic gneiss. All these results provide meaningful clues for the construction of Qiongnan Suture Zone in the research area.