Oligosaccharides are linear or branched carbohydrate compounds composed of two to ten monosaccharide residues connected by glycosidic bonds. They have many health benefits, and can function as sweeteners. Oligosaccharides are a combination of nutritiousness, health care, and dietetic therapy. Compared with polysaccharides, oligosaccharides have several advantages, such as stronger biological activity and easier absorption by the body. In recent years, marinederived oligosaccharides have been proven to have a variety of biological activities, such as antioxidant, anti-tumor, antiinflammatory, antibacterial, anticoagulant, and immunity-enhancing activities. They can be widely used in food, medicine, cosmetics, agriculture, aquatic products, and other fields. This paper introduces four major marine-derived oligosaccharides, including N-acetyl chitooligosaccharide/chitooligosaccharide, alginate oligosaccharides, agarooligosaccharides, and carrageenan oligosaccharides, and presents a brief description of their sources, structural characteristics, various biological activities and applications. It is expected to provide a reference for the high-value utilization of marine polysaccharide resources and the in-depth development of marine oligosaccharides.