Heavy metals in the wrong place at the wrong time and in wrong concentration can be extremely noxious. Metals are integral components of the environment and of living matters. Some have beneficial biological influence, when present in certain concentration. The capacity of organisms to accumulate metals from the environment is well known, although variations exist in the extent of accumulation between species. The levels of metals in the organisms could be used as an index in assessing the quality of the environment. Further-more, the presence of heavy metals like Cd, Pb and Hg in the marine environment has strong effects on the ecology of the area affecting, shifting (or) destroying, sensitive populations leaving hardy organisms to dominate and proliferate in great number. Concentration of heavy metals in the seawater and animal tissues may not be high enough to kill the organisms but are presumably sufficient to destroy their food and have physiological, teratogenic, mutagenic and carcinogenic effects on organisms. Therefore, it is essential to study the bio-accumulation of metals in some organisms of ecological importance. Present study has been undertaken to understand the distribution pattern of heavy metals of Ascidians in Vizhinjam Bay.