The marine macro-alga Nizimuddinia zanardini was harvested from Persian Gulf to assess its biomass for ethanol, biogas and sodium alginate production. The biomass was contained 49.5 and 3.6 mass percent extracted in water and ethanol, respectively. 15.5 W% of mannitol was non-structural and it was extracted from biomass by water. One kilogram of biomass contained 90, 171.2, 100, 150 and 115.2 grams of glucane, mannitol, protein, algenic acid and potassium, respectively. Hydrolysis of the macro-alga was investigated in two stages to evaluate the conversion of cellulose and hemicelluloses in biomass to the corresponding monomeric sugars. These two stages included dilute sulfuric acid pretreatment and enzymatic hydrolysis. The biomass was first subjected to dilute sulfuric acid and hot water pretreatments at 121 °C and then to enzymatic saccharification (45 °C , pH 4.8) for different retention times. The results showed the ability of the first stage hydrolysis in depolymerization of acetyl groups to acetic acid with a maximum yield of 90.8% (based on total acetyl groups content) at 7% (w/w) acid concentration for 45 min and depolymerization of acetyl groups resulted in hydrolysis of hemicelluloses. However, the yield of glucose from glucane was relatively low in the acid hydrolysis. Under these conditions, no hydroxymethyl furfural (HMF) produced and formation of furfural at 5% solid loading was lower than10%. Solid residue of this pretreatment contained 73.3% and 88.9% of algenic acid and glucane, respectively (based on total algenic acid and glucane content). Solution obtained from the dilute acid pretreatment contained 100% of protein hydrolysate and potassium content of biomass. Solid residue of hot water pretreatment was containing 100% and 99% of algenic acid and glucane (based on total algenic acid and glucane content) and Solution obtained from hot water pretreatment contained 100% and 98.4% of protein hydrolysate and potassium content of biomass, respectively. The results of this study indicated that the yield of glucose in enzymatic hydrolysis stage increased by hot water and dilute acid pretreatment from 29.8 to 82.5 and 72.7 gram in one kilogram of dry biomass, respectively. Sugar solution obtained from enzymatic hydrolysis was then subjected to anaerobic fermentation by S . cerevisiae . It was possible to obtain a fermentation yield of 30.5 and 34.6 g/kg, based on the total solid of biomass, by using 7% (w/w) sulfuric acid solution at 120°C for 45 min and 60 min hot water pretreatments and saccharification with two commercial enzymes (cellulose and ?-glucosidase). The yield of ethanol was 0.42 gram in one gram of glucose in fermentation stage. Five minute hot water pretreatment at 121°C was used in order to increase the biogas yield and mole fraction of methane. Solid and liquid of this pretreatment was subjected to biogas production and the yield of methane was increased from 121.7 ml in one gram of volatile solids of biomass for untreated to 131.7 ml for treated. Mole fraction of methane produced in this process increased from 0.52 for treated to 0.535 for untreated. Volatile solids of biomass was 70%W. Keywords: Biogas, ethanol, macroalgae, mannitol, potassium, pretreatment, sodium alginate.