The Porphyridiun cruentum (P.cruentum) are the only unicellular marine microalga in Rhodophyta, which can synthesize and secrete extracellular polysaccharides (EPS) into culture liquid when cells are grown in steady-state culture. The yield of EPS usually correlates with the culture condition of microalga. There have been made some progress about cultivation and bioactive compounds of P. cruentum. However, the researches about the molecular modification of P. cruentum polysaccharide, especially the r...