This paper presents one of the main study results of the co-operative project between Vietnam and Germany on oceanography which was carried out by Institute of Oceanography. Nhatrang, Vietnam. Phase -1 (2003-2006): study on the structure, variation and ecology-environmental effects of Vietnamese upwelling area. Phase-2 (2007-2010): study on the hydrolitho-dynamic, and ecology-environmental features in the Mekong River mouth area and the interactive processes between Mekong River mouth and upwelling water masses. Using water mass analysis, remote-sensing technique and modeling methods, study results show that the features of nearshore bathymetry, tide, river discharge and monsoonal circulation along the west coast of the East Vietnam Sea are the main causes of the interactive processes between Mekong River mouth and upwelling water masses. Preliminary studies show that the interactive processes extend to the area between Binh Thuan and Ca Mau and from the coast to Phy Quy and Con Dao islands.