Marine algae, which make up about 80% of the world's living organisms, contain many energy sources, such as sugars and lipids. Therefore, the possibility of utilizing structural carbohydrates from marine algae for bioethanol production has been studied. In order to obtain monosaccharides, Undaria pinnatifida, Chlorella vulgaris, and Chlamydomonas reinhardtii were used for the saccharification experiments. The pretreatment was carried out by dilute acid hydrolysis and enzymatic treatment. To find the optimal conditions, experiments were performed at several temperatures, acid concentrations, pH conditions and durations. To test bioethanol production, several ethanolic E. coli W3110 strains, which were developed previously, were used. The maximum yield of bioethanol, 0.4 g ethanol/g biomass, was achieved with pretreated C. vulgaris and E. coli SJL2526, derived from wild-type E. coli W3110 and which includes the adhB, pdc, galP, and glk genes.