Abstract: As a by-product of sea cucumber processing, viscera are often discarded but they contain structurally complex polysaccharides with potential biological activities. However, the structural characteristics of these polysaccharides and their relationship with antioxidant activity remain insufficiently understood. Thus, we extracted Holothuria leucospilota viscera polysaccharides (HLVP) using papain enzymatic hydrolysis and preliminarily characterized their structures through chemical analysis and Fourier transform infrared spectroscopy (FTIR). Subsequently, we evaluated the antioxidant activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assays, and the ferric reducing antioxidant power (FRAP) method. Finally, we investigated the effect of the polysaccharide on α-glucosidase activity through in vitro enzyme activity assays. The results show that HLVP contained 43.79% total sugar, 8.46% uronic acid, 3.17% protein, and 0.85% total phenol. FTIR analysis reveals the presence of typical polysaccharide functional groups, including hydroxyl (−OH), methylene (−CH₂), carbonyl (C=O), ether (C−O−C), and α-glycosidic bonds. The activity studies indicate that HLVP exhibited in vitro antioxidant capacity, with DPPH and ABTS radical scavenging activities and FRAP values increasing in a concentration-dependent manner. Moreover, HLVP showed a significant activation effect on α-glucosidase activity, which also demonstrated good concentration dependence. These findings provide an experimental basis for further elucidating the structure-function relationship of HLVP and exploring their potential applications in functional foods or glucose metabolism regulation.