Fucoidan, a natural sulfated polysaccharide extracted from seaweed, has been widely used in pharmaceutical field due to its excellent biological activities including antiviral, anticancer, antioxidant, anticoagulant, etc. Therefore, investigating the new natural sources of fucoidan has been received growing attention recently. This study reported for the first time the isolation, purification, characterization, and biological activities of fucoidan from Ceratophyllum submersum (FCS). The molecular weight of obtained FCS was 9.7 kDa, composed of fucose (42.11%) and sulfate (16.38%). The FCS contained (1 -> 3)-alpha-L-Fucopyranose and beta--D-galactose bond in the structure. In addition, FCS showed strong antioxidant properties against 2,2-diphenyl-1-picrylhydrazyl, 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid), and reactive oxygen species radicals with inhibitory concentration 50 values were 765.48 ppm, 845.31 ppm, and 1760.00 ppm, respectively. The FCS also performed good antibacterial, antifungal, anticoagulant and anti-inflammatory activityies. Especially, it expressed a better inhibition activity on breast cancer cell line (MCF-7) than that on liver cancer cells (HepG2), lung cancer cells (NCI-H460), and cervical cancer cells (HeLa). FCS demonstrated potential utility in functional food, cosmeceutical, and pharmaceutical industries. In the trend of discovering new sources for fucoidan with outstanding bioactivities, this report would contribute a basic platform and valuable information for further studies on fucoidan from C. Submersum.