The Gulf of Mannar and Palk Bay of South East Coast are rich in seaweed resources. Seaweeds are one of the important marine living renewable resources and are used for human consumption, animal feed and as manure in several countries. So, some of the representatives from Chlorophyta, Phaeophyta and Rhodophyta were investigated in the present study for biochemical composition. The macroalgae showed varied quantities of biochemical constituent are namely Amino acids, Proteins, Lipids, Carbohydrates and Phenol. High concentration of Glutamic acid and Aspartic acid was recorded in red algae Acanthopora spicefera 17.4 % and 15.7% respectively and lowest value of Methionine was recorded in all species except Chnoospora minima (3.1%). Highest protein was recorded in Acanthopora spicefera 18.9% and low value was recorded in brown algae Padina gymnospora (10.5%). Lipid content was high in green algae Caulerpa recemosa (19.1%) and low value in Ulva faciata (0.5%). Carbohydrate content was high in green algae Caulerpa racemosa 83.2% and low in Chnoospora minima 28.5%. In phenol the highest value in Acanthopora spicefera and lowest in Caulerpa racemosa 14.3%.