ABSTRACT Red seaweed possess various sulfated polysaccharides (SPs) that could potentially be exploited as bioactive agents for medical and industrial applications. Crude polysaccharides from the red algae Corallina officinalis (SP1) and Pterocladia capillacea (SP2) were extracted and characterized according to their chemical content and their antioxidant, anti-inflammatory, anticoagulant, antibacterial, antifungal, and antifouling activities. The isolated polysaccharides contained low levels of protein and high levels of carbohydrate and sulfate. The extracted SPs were characterized by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectral data and revealed that SP1 is composed of carrageenan, while SP2 is composed of polysaccharides containing sulfated galactans plus κ- and ι-carrageenan. Both isolated SPs exhibited all the tested biological activities but those of SP2 were superior. These results reflect the beneficial effects that red algal polysaccharides have as a natural renewable bio-product and that there is a significant relationship between polysaccharide structure, sulfate content and their biological properties. Further studies should be undertaken on the fractionation and characterization of polysaccharides extracted from species of red seaweed in addition to experiments to verify the efficiency of the extracted SPs for food and medical uses in vivo.