The present paper deals with the distribution of seaweeds and seagrasses during the deep sea survey conducted in the first sector from Kattapadu to Tiruchendur in Tamil Nadu coast between December 1986 and March 1987 covering an area of 650 sq.km. In this survey 58 species of marine algae were recorded of which 7 belong to Chlorophyta 12 to Phaeophyta and 39 to Rhodophyta. Three species of seagrasses viz. Cymodocea serrulata. Halophila ovails and H. ovala were also recorded at the depths ranging from 5.5 to 21.5 III Halim eda macroloba, Dictyota barlayresiana, D. Maxima, Gracliaria corticata var. corticala, G. edulis, Sarcodia indica, Sarconema filiform e, Soliena robusta, flypnea esperi and H. Valentiae were found to be dominant and widely distributed.