Cancer chemopreventive effects can be exerted through the induction of phase II detoxification enzymes and the inhibition of inflammatory responses. In this study, the cancer chemopreventive effects and anti-inflammatory responses of 30 seaweed extracts were examined. The extracts of Dictyota coriacea and Cutleria cylindrica exhibited the high chemoprevention index, having 4.36 and 4.66, respectively. They also activated antioxidant response element at $100;{mu}g/mL$ by about 3-fold while did not activate xenobiotic response element. Seven seaweed extracts, Ishige okamurae, Desmarestia ligulata, Desmarestia viridis, Dictyopteris divaricata, D. coriacea, Sargassum horneri, and Sargassum yezoense, showed significant inhibition on nitric oxide (NO) and prostaglandin $E_2$ ($PGE_2$) production in a dose-dependant manner in $5-20;{mu}g/mL$. These seaweed extracts could be used as food materials for cancer chemoprevention. D. coriacea could contain potential chemopreventive agents not only that regulate genes via an ARE-dependent mechanism but also prevent the inflammation through inhibition of NO and $PGE_2$ production.