This study investigated the effect of sonication time on the stability and antioxidant activity of fucoidan-loaded double emulsion. Increasing the duration of ultrasound treatment from 4 to 10 minutes significantly increased the emulsion's resistance to separation (from 60% to 93%) and increased the antioxidant activity of DPPH (from 60% to 92%). The optimized 10 min sonicated emulsion had a small droplet size of 460 nm. The research was carried out with financial support from the Russian Science Foundation grant 22-76-10049.