Fucoidan, extracted from Undaria pinnatifida (U. pinnatifida), has been extensively studied because of its wide biological activities. However, antioxidative activities of fucoidan extracted from Miyeokgui have not been yet examined in the zebrafish model. Therefore the present study was designed to evaluate in vitro and in vivo studies on antioxidative activities of fucoidan extracted from Miyeokgui by using 0.1 M hydrochloric acid (MAF). We found that MAF reduced the production of intracellular reactive oxygen species (ROS) in the 2, 2’-azobis dihydrochloride (AAPH) induced oxidative stress in Vero cells. Furthermore, the protective effect of MAF was examined against AAPH-induced oxidative stress in zebrafish model. MAF possesses a protective effect against AAPH-induced toxicity in zebrafish embryos. In addition, MAF significantly reduced AAPH-induced ROS production and lipid peroxidation in zebrafish embryos. These results proved that MAF has antioxidant activities both in vitro Vero cells and in vivo zebrafish model.