This review article by Ya-jing Chen et al. provides a comprehensive overview of oligosaccharides, focusing on their preparation, structural characterization, biological activities, and nutritional applications. Oligosaccharides, low-molecular-weight carbohydrates, are extracted from natural products or synthesized chemically and enzymatically. They exhibit various physicochemical and physiological properties, making them valuable in functional foods and medicinal applications. The article highlights the importance of functional oligosaccharides as dietary fiber and prebiotics, which can improve gut microecology, exert antitumor, anti-inflammatory, antioxidant, and lipid-lowering effects. The review also discusses the industrial applications of oligosaccharides, particularly in the food industry, and their potential in human nutritional health. Key topics include the preparation methods (physical, chemical, and biological), structural characterization techniques, and the biological activities of different types of oligosaccharides. Additionally, the article explores the use of herbal oligosaccharides, their sources, and specific biological activities. Finally, it addresses the application of oligosaccharides in food nutrition, including improving food flavor, promoting food health, and extending shelf life. The authors emphasize the need for further research to optimize the extraction and characterization techniques, develop composite oligosaccharide products, and establish systematic platforms for precise extraction and characterization.This review article by Ya-jing Chen et al. provides a comprehensive overview of oligosaccharides, focusing on their preparation, structural characterization, biological activities, and nutritional applications. Oligosaccharides, low-molecular-weight carbohydrates, are extracted from natural products or synthesized chemically and enzymatically. They exhibit various physicochemical and physiological properties, making them valuable in functional foods and medicinal applications. The article highlights the importance of functional oligosaccharides as dietary fiber and prebiotics, which can improve gut microecology, exert antitumor, anti-inflammatory, antioxidant, and lipid-lowering effects. The review also discusses the industrial applications of oligosaccharides, particularly in the food industry, and their potential in human nutritional health. Key topics include the preparation methods (physical, chemical, and biological), structural characterization techniques, and the biological activities of different types of oligosaccharides. Additionally, the article explores the use of herbal oligosaccharides, their sources, and specific biological activities. Finally, it addresses the application of oligosaccharides in food nutrition, including improving food flavor, promoting food health, and extending shelf life. The authors emphasize the need for further research to optimize the extraction and characterization techniques, develop composite oligosaccharide products, and establish systematic platforms for precise extraction and characterization.