Thoothukudi. popularly called as ‘Pearl city’ has lost its charm due to industrialization. Thoothukudi. sea water has become contaminated due to the effluent discharges from several industries. The Thoothukudi. sea water is contaminated and polluted due to the untreated sewage drained into the sea from Industries and factories. The outcome is that there is higher concentration of toxic heavy metals which affect the marines species especially Sardinella Longiceps. This paper is a report of research work carried out in the Threspuram Area of Thoothukudi. which is a part of Gulf of Mannar. An Investigation was carried out to assess the heavy metal substances(Cu, Ni, Fe, Co, Mn, Cr and Zn) in the commercially important fish species Sardinella Longiceps. The accumulation was found in tissues of muscles, liver, kidney and gills. Concentration of heavy metal substances were studied in sea water, sediment and the fish Sardinella Longiceps and the results showed that the concentration of heavy metals was found in the order of Fe>Mn>Cu>Pb>and Zn.