Due to the reduction and concerns about the future of fossil fuels, extensive research has been carried out to develop renewable alternatives with less greenhouse gas emissions. One of the renewable sources is bioethanol, which can be produced from cellulosic biomass cultivated in water and soil. Bioethanol production from algae is referred to the third-generation biofuels. The benefits of this generation include the use of non-edible sources with high production efficiency and no need for freshwater and fertile soil for their growth. In this study, Sargassum angustifolium macroalga was used as the raw material for bioethanol production. This brown alga was harvested from Persian Gulf in summer and winter. It contained appreciable amounts of alginate as a valuable ingredient with many applications in various industries. Also, it composed of cellulose with different properties than lignocellulosic plants that do not required complex pretreatment for efficient biological conversions. Accordingly, at first, alginate was extracted from the alga, which is a valuable byproduct of ethanol production. This extraction process acted as a type of pretreatment for subsequent ethanol production. Alginate extraction was conducted with acid treatment (0.2 N hydrochloric acid) followed by an alkaline extraction (2% w/w sodium carbonate). The amounts of sodium alginate obtained were 24.40% and 22.40% for the samples harvested in summer and winter, respectively. The corresponding rates of solid residue recovery in the extraction process were 31% and 16.5% for the summery and wintery alga samples. In order to evaluation the effect of alginate extraction from alga, the solid residue from extraction and raw algal samples were subjected to enzymatic hydrolysis by commercial cellulase cocktail, Cellic CTec2. Extraction of alginates from alga increased the hydrolysis efficiency from 32.3 to 53.2 percent and from 32.8 to 61.9 percent in summery and wintery alga, respectively. In order to produce ethanol, the raw algal samples and wastes from alginate extraction were subjected to non-isothermal simultaneous saccharification and fermentation using the Saccharomyces cerevisiae for ethanol fermentation. The results showed that the summery algal samples produced 124.8 and 172.2 g/kg ethanol, where the wintery samples produced 148.4 and 187.2 g/kg ethanol from raw algal and solid residue of alginate extraction process, respectively. The final step was replacement algal extract with yeast extract in the ethanol production process. Algal extract was obtained in alginate extraction from the alga in two stages, i.e., before and after alkaline extraction. The two types of algal extracts were replaced with yeast extract and the ethanol production was determined. The use of wintery algal waste using the algal extract (after alkaline extraction) instead of yeast extract improved ethanol yield by 3.48% and the ethanol production increased to 197.20 g/kg wintery algal waste. Key words: Bioethanol, Brown macroalgae, Sargassum angustifolium , Sodium alginate