Abstract: Tilapias are prone to spoilage due to protein oxidation during cold storage, making it crucial to adopt appropriate treatments to extend their refrigerated shelf life. This study focused on tilapia and investigated the effects and potential mechanisms of oligomeric proanthocyanidins (OPC)-agaro oligosaccharide (AGOS) on the changes in myofibrillar protein during cold storage. By measuring indicators such as myofibrillar protein concentration, total sulfhydryl content, carbonyl content, microstructure, enzyme activities and spatial structure, a comprehensive evaluation was conducted on the impact of OPC and AGOS on the oxidation of myofibrillar protein in refrigerated tilapia fillets. The results demonstrated that the 0.2% OPC+0.5% AGOS compound group more effectively inhibited the decrease in myofibrillar protein concentration and total sulfhydryl content compared to the untreated group. In the later stages of storage, the compound group exhibited less alteration in the organizational structure of myofibrillar protein and maintained finer tissue gaps. During storage, this group effectively suppressed the increases in polyphenol oxidase (PPO) and peroxidase (POD) activities, while mitigating the decreases in Ca²⁺-ATPase, superoxide dismutase (SOD), and fatty acid synthase (FAS) activities. Additionally, the compound group could preserve the α-helix structure and maintain the stability of the protein's tertiary structure. In conclusion, the combination of oligomeric proanthocyanidins and agaro oligosaccharide can effectively maintain the spatial structure of myofibrillar protein in tilapia fillets and inhibit protein oxidation during storage. This approach offers a novel natural preservation strategy for enhancing the freshness and quality of aquatic products.