BACKGROUND: Partially replacing NaCl with KCl under ultrasound can improve muscle quality and reduce oxidative degeneration of myofibrillar proteins in semi-dried large yellow croaker (Larimichthys crocea). Myosin, the most important protein in myofibrillar protein, plays an important role in muscle quality. Hence, the present study aimed to investigate the effect of replacing NaCl with KCl on the physicochemical properties of myosin derived from large yellow croaker under ultrasound. Furthermore, the application potential of ultrasound to low sodium salt products was evaluated. RESULTS: The results showed that ultrasound treatment reduced the aggregation and particle size of myosin. By contrast, at high salt concentrations, myosin oxidation was inhibited and protein aggregation increased. This led to an increase in particle size and a decrease in stability and surface hydrophobicity of myosin. Interestingly, KCl increased myosin solubility and promoted protein unfolding, the excess of which exposed some active sites, leading to oxidative destruction of the proteins. In the present study, the chromophore and surface hydrophobic groups of myosin were exposed as a result of the KCl-mediated unfolding of the α-helices of myosin after the partial replacement of NaCl with KCl. This improved the structural stability of myosin and reduced its oxidative damage. CONCLUSION: The findings of the present study show that the presence of NaCl and KCl in the system was more conducive to protecting the key role of myosin in the muscle tissue compared with NaCl alone. Additionally, the study provides insights into the mechanism of K