Oligosaccharides are low-molecular-weight carbohydrates between monosaccharides and polysaccharides, extracted from natural sources or synthesized chemically or enzymatically. They have important physicochemical and physiological properties, used as dietary fiber and prebiotics to improve gut microecology, exert antitumor, anti-inflammatory, antioxidant, and lipid-lowering effects. Functional oligosaccharides are important in food and medicinal chemistry, with applications in food industry and human nutrition. They are divided into digestible and indigestible types, with indigestible ones being non-digestible oligosaccharides, including fructooligosaccharides, isomaltooligosaccharides, etc. Marine oligosaccharides, human milk oligosaccharides, and glycosaminoglycan oligosaccharides are also gaining attention. Oligosaccharides are prepared through physical, chemical, and biological methods, with physical methods being preferred for minimizing hazardous chemicals. Chemical methods involve multiple functional groups and complex synthesis, while biological methods use enzymes for efficient synthesis. Structural characterization of oligosaccharides involves methods like NMR, IR, and HPLC. Bioactivity includes antioxidant, anti-inflammatory, antitumor, and antihyperlipidemic effects, with chitosan oligosaccharides showing significant antitumor activity. Oligosaccharides improve gut flora, regulate microbiota, and have prebiotic properties. Herbal oligosaccharides, such as those from Ganoderma lucidum and Panax ginseng, have various biological activities. Oligosaccharides are used in food to improve flavor, health, and shelf life, with applications in beverages, dairy, and health products. They are also used in animal feed and health products. Safe dosage guidelines are needed for different oligosaccharides, with recommendations varying by country. Future research should focus on structural analysis, quality control, and synthesis methods to develop functional oligosaccharides for food and medicine. Oligosaccharides are important in functional foods and nutraceuticals, with broad market prospects.Oligosaccharides are low-molecular-weight carbohydrates between monosaccharides and polysaccharides, extracted from natural sources or synthesized chemically or enzymatically. They have important physicochemical and physiological properties, used as dietary fiber and prebiotics to improve gut microecology, exert antitumor, anti-inflammatory, antioxidant, and lipid-lowering effects. Functional oligosaccharides are important in food and medicinal chemistry, with applications in food industry and human nutrition. They are divided into digestible and indigestible types, with indigestible ones being non-digestible oligosaccharides, including fructooligosaccharides, isomaltooligosaccharides, etc. Marine oligosaccharides, human milk oligosaccharides, and glycosaminoglycan oligosaccharides are also gaining attention. Oligosaccharides are prepared through physical, chemical, and biological methods, with physical methods being preferred for minimizing hazardous chemicals. Chemical methods involve multiple functional groups and complex synthesis, while biological methods use enzymes for efficient synthesis. Structural characterization of oligosaccharides involves methods like NMR, IR, and HPLC. Bioactivity includes antioxidant, anti-inflammatory, antitumor, and antihyperlipidemic effects, with chitosan oligosaccharides showing significant antitumor activity. Oligosaccharides improve gut flora, regulate microbiota, and have prebiotic properties. Herbal oligosaccharides, such as those from Ganoderma lucidum and Panax ginseng, have various biological activities. Oligosaccharides are used in food to improve flavor, health, and shelf life, with applications in beverages, dairy, and health products. They are also used in animal feed and health products. Safe dosage guidelines are needed for different oligosaccharides, with recommendations varying by country. Future research should focus on structural analysis, quality control, and synthesis methods to develop functional oligosaccharides for food and medicine. Oligosaccharides are important in functional foods and nutraceuticals, with broad market prospects.