Granitoid in the Rong, Bach Ho oilfield basement of the Cuu Long Basin, south Vietnam consists of diorite, granodiorite and less granite. The rocks are fractural, catac1astic and dark grey in colour. Biotite and horblende are main colour mineral in the rocks. These granitoids were previously assigned to the T3-J1 Hon Khoai or C3-P1 Ben Giang - Que Son complexes based on the K-Ar age data. In order to elucidate the emplacement time of the granitoids in the Cuu Long Basin and their geological implications, zircon separated from granitods collected in the Rong oil field, Bach Ho oil field basement for U-Pb sotope analyses and yielded a mean 206Pb/238U age of 94.2 Ma and 115.5 Ma, respectively. Regression of 3 and 9 data points defined whole rock Rb-Sr isochrons that gave ages of 79.5+5.6 Ma with MSWD = 1.09 for the Rong granite and 130+21 Ma for the Bach Ho granitoids with MSWD = 385, respectively. The age data from Bach Ho granitoids yielded an errisochron and due to mobility of Rb, therefore, the U-Pb zircon ages of 94.2 and 115.5 Ma, corresponding to the early Cretaceous, were considered as the best emplacement ages of the granitoids. These ages are similar to those of Deo Ca and Dinh Quan granitoids in the Da Lat zone and indicate magmatism took place during Cretaceous time. This enables us to extend the search areas for oil and gas along the coast of Vietnam where Early Cretaceous granitoids are present.