Abstract: Methods of separation and purification of nitrogenase of blue-green algae were improved. With anaerobic preparative polyacrylamide gel electrophoresis instead of usual chromatogrophy, Mo-Fe protein was purified to electrophoresis purity. The procedure was simplified and the duration of process was shortened.Gel filtration of the Mo-Fe protein resulted a molecular weight of 360,000. SDS electrophoresis showed that it was compoed of 4 identical subunits each having a molecular weight of 90,000. The amino acid, residues/mole Mo-Fe protein were 3290. Acidic amino acids were predominant. The Km for acetylene was found to be 3.33×10-3 atmospheres. The isoelectric point was 5—5.5. UV/visible absorption spectrum of Mo-Fe protein was similar to that of Mo-Fe protein from bacterial source. Salt inhibited nitrogenase from blue-green algae more strongly than that from bacteria.