Abstract: With the increasing research of marine polysaccharides, people are attaching importance to the research of marine oligosaccharides. Marine oligosaccharides are prepared by the degradation from marine polysaccharides with different methods. They have the characteristics of abundant sources, small molecular weight and unique structure. The degraded marine oligosaccharides have stronger biological activities than marine polysaccharides, such as anti-oxidation, anti-tumor, immunomodulation, anti-inflammatory, regulating intestinal microorganisms, etc. Therefore, they are widely used in food, health products, medicine and other fields. At present, the methods of marine oligosaccharides preparation include: Chemical degradation, physical degradation and enzyme degradation. In order to understand the research progress, promote the application and development of marine oligosaccharides, in this paper, the preparation methods and physiological activities of marine oligosaccharides are reviewed, which is expected to provide references for the further research and development of marine oligosaccharides.