In Eastern Sea (South China Sea), Jurassic - Cretaceous magmatic intrusives are discovered, they were cutting the Pre-Cenozoic sedimentaries. The Cenozoic volcanic basalts are strongly distributed together with Cenozoic sedimentaries. The paper concerns only the volcanic activities with description on their geology, chemistry, geochemistry, isotopic ages and their forming mechanism. In fact, the main topic of the paper is dealt with the forming mechanism of basalt in the dynamics of the opening of Eastern Sea in particular, and of South China Sea in general. Keywords: Cenozoic; Magmatism; Eastern Sea. 1. Generality on cenozoic geology of Eastern Sea* The geomorphology and.