Agar, carrageenan and alginate are high valued seaweed polysaccharides, which are used as gelation and thickening agents in different food, pharmaceutical and biotechnological industries. The annual global production of the polysaccharides has recently reached 100,000 tons with a gross market value just above US$ 1.1 billion. In Sri Lanka although several seaweed species are available, there is no systematic study on comparison of method of extraction, yield and physicochemical properties of polysaccharides from seaweeds. Seaweed species Gracilaria edulis, Gracilaria verrucosa, Kapphaphycus alverazi and Sargussum wightti were collected from North and South coast of Sri Lanka. Gracilaria edulis and Gracilaria verrucosa were used for agar extraction with acid and alkaline treatments. Carrageenan was extracted from Kapphaphycus alvarezii using alkaline treatments. Three types of carrageenan (kappa, iota, lambda) were separated using freeze thawing, jelly pressing and alcohol precipitation methods respectively. For the extraction of alginates from Sargussum wightti samples were treated with acid and alkaline and hot and cold extraction methods were used. Some of the above physiochemical properties were compared with commercial available products.

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