Exopolysaccharides (EPS) from cell-free Porphyridium cruentum media were concentrated then purified (diafiltration) on a 0.14 µm 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 bar for respectively cross-flow velocities inside the membrane lumen equal to 2.5, 3.3 and 4.2 m.s-1; 49.7 L.h-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 to 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.