Yeast mannan, an essential polysaccharide derived from the cell walls of yeast, has garnered significant interest in recent years owing to its diverse biological functions and potential health benefits. This review intends to thoroughly explore the structural characteristics of yeast mannan, elucidating the manner in which its unique molecular architecture affects its functional properties. Recent studies highlight its multiple health contributions, including notable antioxidant effects, immunomodulatory functions, and the enhancement of gastrointestinal health. However, challenges remain in fully elucidating the relationship between structure and function, particularly regarding the differential regulatory influences of specific types of glycosidic bonds on immunomodulatory activities, as well as improving extraction and application techniques for industrial use. By integrating the most recent research findings, this article aims to emphasize the bioactive potential of yeast mannan and examine its prospective applications in nutraceuticals and functional foods. Additionally, the review identifies existing knowledge gaps and suggests avenues for future research aimed at optimizing its therapeutic potential, thereby establishing a scientific basis for both academic research and commercial application. In particular, a comprehensive understanding of the structure-activity relationship (SAR) related to yeast mannan, especially the correlation between glycosidic bond specificity and biological efficacy, remains critical. Furthermore, assessing the toxicological risks associated with mannan derivatives is another vital yet often neglected aspect necessary for the safe industrial application of these compounds.