Fucoidan-degrading enzymes are glycoside hydrolases that hydrolyze fucoidan into low molecular mass fucosan with biological activity or other products. The enzymes have great application value in the preparation of active fucoidan oligosaccharides, biopharmaceutics and disease diagnosis. In this article, the sources, properties, modes of action, structures and applications of fucoidan-degrading enzymes are reviewed, revealing that fucoidan-degrading enzymes are mainly derived from marine microorganisms and marine invertebrates and that the enzymatic properties, substrate specificity, molecular structures and catalytic mechanisms of fucoidan-degrading enzymes vary significantly depending on the species source. Different types of fucoidan-degrading enzymes catalyze different sites of complex fucoidans producing fucoidan oligosaccharides with antioxidant, anti-tumor, anti-thrombotic or other special activities. Therefore, the utilization of fucoidan-degrading enzymes in the preparation of drugs and functional foods has gradually become a research focus in the application field of polysaccharides. This article provides theoretical support for further research on fucoidan-degrading enzymes, and also provides references for the effective development of fucoidan oligosaccharides with special biological functions.