Abstract: Microfossils, including spores, pollen and radiolarian, were found in the Mesozoic which was first encountered in Well MZ-1-1 in the north of the South China Sea. The geological time of the spore and pollen assemblage dominated by Classopollis and Cyathdites is given as the middle Jurassic, which was recovered from the interval 2 187~2 388 m of Well MZ-1-1. The siliceous rocks occurring in the interval 1 725~1 887 m of this well contains late Jurassic to early Cretaceous radiolarian assemblages, mainly including Caneta hsui,Loopus primitivus,Dibolachras sp. cf. D. apletopora. The results of microfossil analysis have demonstrated the occurrence of marine Jurassic and Cretaceous in the north of the South China Sea. The spore and pollen assemblage dominated by Classopollis and Cyathdites reflects the tropical to subtropical coastal vegetation and coastal marshland that developed in the north of the South China Sea during the middle Jurassic. The deposition environment changed greatly and the deep water reigned in this region during the late Jurassic to early Cretaceous.