In this study, we investigated the oxidative and structural effects of red sour soup and ultrasound-assisted marination on beef myofibrillar proteins (MPs). The results demonstrated that marinating with red sour soup could alter MPs structure and oxidative properties, promote MPs aggregation, and increase protein particle size. Compared to traditional static marination, ultrasound-assisted marination significantly elevated protein oxidation levels (P <
0.05), as shown by the increase in carbonyl and reduction in sulfhydryl (P <
0.05). Secondary and tertiary protein structures revealed that ultrasound decreased the α-helix and increased the β-sheet, promoting the exposure of hydrophobic groups. Particle size significantly decreased with increasing ultrasound power (P <
0.05). The SDS-PAGE further illustrated that appropriate ultrasound treatment (320 W) alleviated protein cross-linking and aggregation induced by organic acids. Overall, this study showed that ultrasound ameliorated the effects on protein structure during marinating due to the acidic conditions of red sour soup, offering a theoretical foundation for its application in meat processing.