A high-pressure liquefied extract of marine algae for producing bioethanol and a method of producing the liquid extract from marine algae under high pressure, and a method of producing the bioethanol from the high-pressure liquid extract by fermentation with yeast are disclosed. According to the production method of bioethanol using marine algae, the high-pressure liquefied extract can be obtained in high yield and fermentation time can be also reduced. Consequently, the yield of bioethanol is increased. Furthermore, the method gives economical and environmentally friendly values from natural marine algae.