Alginic acid and alginates have important aplication in food, medicine, pharmacy, dentistry and textile. Since the brown algaes of the South Sea of ??Iran (the Chaharbar area) contain this natural polymer, extraction of the sodium alginate from the brown algae (Nizimuddinia zanardini) optimized using Response Surface Methodology (RSM). Extraction of the sodium alginate from the cell wall of the brown algae perform in 3 steps by acidic and alkaline solutions and then gum was precipitated by ethanol. For optimizing conditions, in acidic step the effect of extraction temperature by Hydrochloric acid(0.2 M) in range 45-100 °C and extraction time in range 0.5-3.5 h , on the dependent variables including: yield, protein and polyphenol of extracted alginate were investigated and after optimization of these factors, in second step (alkaline step) the effect of extraction temperature with Na 2 Co 3 (60-90 °C), extraction time (2-4 h) and solution concentration (2-4 % w/v) on the dependent variables including: yield, polyphenol and apparent viscosity of extracted alginate were studied and factors were optimized. The results showed that in acidic step temperature and time are two major effective factors on yield and quality of extracted alginate and in alkaline step, all factors have effect on yield, polyphenol and apparent viscosity of extracted polymer. The optimized conditions of extraction of sodium alginate from brown algae (Nizimuddinia zanardini) were as follows: temperature: 60 o C, time: 3 h (acidic step) and temperature:60°C,time:2.5h and concentration 3% w/v(alkaline step). After optimization of acidic and alkaline steps, a high-voltage electrical discharge device was used as an acidification pre-treatment. At this stage, the number of electrical discharge and applied voltage were considered as variables and its effect on the rate Extraction efficiency was investigated. The optimal conditions in this method are the use of an electric discharge device with a voltage of 10 kV and 50-times electrical discharge. Sodium alginate from Nizimuddinia zanardini (an Iranian brown algae) was extracted with and without HVED, partially and totally hydrolyzed and analyzed for its biochemical composition. 1 H-NMR spectroscopy, SEC-MALLS, HPAEC and FT-IR were performed to determine its structure and its physico-chemical properties. This alginate has a M/G ratio of 1.1, a molecular weight of 103 kDa, a polydispersity index of 1.22, and an intrinsic viscosity of 342 mL/g. Its antioxidant activity was tested by DPPH radical scavenging showing its potential for food preservation. Rheological properties of solutions of this alginate with concentrations between 1 and 5 % (w/v) in water and 0.5 M NaCl were investigated indicating a Newtonian fluid type behaviour in water and a shear thinning fluid type behaviour in NaCl solutions. The influence of pH on 2.0% (w/v) alginate solution flow behaviour was investigated. Solution at pH equal to 7.0 had a Newtonian behaviour, an intermediary behaviour between Newtonian and non-Newtonian shear thinning at pH 6.0 and 5.0 and a clearly shear thinning behaviour at lower pH (4.5 and 3.0). Using pre-treatment of electrical discharge only improves the antioxidant properties and in the remaining cases, led to a loss of quality due to the breakdown of the bonds and the molecular chain in sodium alginate. Key words Sodium alginate, Extraction optimization, Iranian brown algae, Nizimuddinia zanardini , Physico-chemical characteristics, Rheological properties Antioxidant activity