In recent years, sulfated polysaccharides from marine algae have been demonstrated to have many activities including antioxidant activities. But whether degraded sulfated polysaccharides from Chondrus ocellatus have antioxidant activities, and what effects their sulfate content may have on those activities has not been reported. The aim of this study is to explore the antioxidant activities of λ-carrageenan fractions from edible red seaweed Chondrus ocellatus. In the present study, λ-carrageenan from Chondrus ocellatus was degraded by microwave, yielding five products of different molecular weights. Three sulfated polysaccharide fractions (CF1, CF2, and CF3) were isolated from one of the degraded λ-carrageenans (PC2) by anion-exchange column chromatography. In this study, the effects of the three polysaccharide fractions on hydroxyl radicals, superoxide radicals, organic free radical DPPH, H2O2 induced hemolysis of rat erythrocytes and lipid peroxidation in rat liver microsome were investigated.