Based on the studied results in 2010, and the comparison with the recent studies (2007-2009), it showed that the contaminations by the DDTs compounds in sediment substrate of Nha Trang Bay is a huge and much larger than in recent years. It also showed that the toxicants highly accumulated at the sediment bottom in river mouths (especially in Cai river transect) such as: at C3 station (IDDTs concentration was 20.109pg/kg) and C6 station (IDDTs concentration was 15.206pg/kg). The DDT contaminations were higher than the level of limitation of the PEL about 3 to 4 times (evaluation based on the standard guidelines of CCME EPC-98 EC). The accumulation of DDTs compounds }\'ere clearly present in the sediment cores with the high concentration in top layers, and accumulation trends were continuously occurred in the areas, in spite of the organ-chlorine pesticides is strictly prohibited and reduced in many application for many years ago. Meanwhile, the PCBs in sediment substrate in most of surveyed location were very low. It was demonstrated that the Nha Trang Bay is not affected or contaminated by the sources emission of PCBs to compare with estuaries and other coastal areas of Vietnam. Therefore, it should be a warning of these organic pollution for the marine environment of Nha Trang Bay, because of organic pollutants were caused ecological risk and harmful for human health.