Exopolysaccharides (EPS) from cell-free Porphyridiwn cruentum media were concentrated then purified (diafiltration) on a 0.14 ism ceramic membrane. The influence of cross-flow velocities on filtration performances was investigated. Mean permeate fluxes equal to 49.8, 68.9 and 81.9 L h(-1). m(-2) were obtained during the concentration at 4 bars for respectively cross-flow velocities inside the membrane lumen equal to 2.5, 3.3 and 4.2 m s(-1); 49.7 Lm(-1). M-2 for the diafiltration at 3.3 m s(-1). Permeate fluxes were correctly predicted from polysaccharide concentrations (10% deviation). Volume reduction factors higher than 7.8 were reached. Rejection rates of polysaccharides and proteins varied according to the cross-flow velocities. Thus, the EPS recovery rate or time of filtration could be modulated following the cross-flow velocity. Polysaccharides were concentrated 6.3 to 10.4 times in such a way that the final sugars concentration reached 1.74-2.26 g L-1. Rheological behavior of filtered solutions changed following the concentration progress. More than 80% (w/w) of polysaccharides were recovered while 49% and 99% of proteins and salts were removed respectively. The filtrations allowed reaching a final monosaccharide content of dry matter equal to 48.9% against 0.6% (w/w) initially.