The present invention relates to a composition for preventing and treating acetaminophen induced liver injury comprising the protein extracts from porphyra yezoensis. The protein separated and purified from hot water extracts of porphyra yezoensis and having the molecular weight of 14 kDa measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis manner has an excellent effect for inhibiting the oxidative injury of the liver tissue and the cell apoptosis of the liver cell induced by acetaminophen.