The aim of this study was to assess the total radical trapping antioxidant potential and antigenotoxic effects by comet assay of ethanol extracts of stalked sea squirt, Styela clava, (tunic, substrate, and whole). All extracts of stalked sea squirt effectively scavenged $ABTS^{{cdot}+}$ in a dose dependent manner. Pretreatment with each extract of stalked sea squirt produced significant reductions in oxidative DNA damage at concentrations of 1-50 ${mu}g/mL$, with whole extract of stalked sea squirt showing higher inhibition (16.1 ${mu}g/mL$) of $H_2O_2$ induced DNA damage than substrate or tunic extracts based on $ED_{50}$ values. The addition of 50 ${mu}g/mL$ of stalked sea squirt extracts to human leukocytes after oxidative stimulus (200 ${mu}M$ $H_2O_2$) for 5 min positively influences the kinetics of DNA repair during 24 hr of incubation. These results indicate that the ethanol extracts of tunic, substrate, and whole stalked sea squirt have significant antioxidant activities that protect against oxidative DNA damage and improve DNA repair capacity.