The persistent organic pollutants PCBs and PAHs were determined in three components water, sediment and tissues of Ha Long bay in Vietnam (in October 2008 and February 2009). Results show that the concentration in water: PCBs are 51.09 - 62. 31ng/l, PAHs are 5.69 - 8.66 ug/l
in surface sediment: PCBs are 3.31 - 6.92 ug/kg dry, PAHs are 99.04 - 100.47 ug/kg dry and in tissues (clam, shrimp, fish): PCBs are 37.39 - 173.63 ug/kg dry, PAHs are 2034 - 2583 ug/kg dry. The pollution level of PCBs and PAHs in each sea components vary to season of year, and the bio-accumulation capacity of them elevate by fauna in Ha Long bay's food chain.