A symbiotically associated cyanobacterium (Anabaena azollae) was isolated from Azolla pinnata and cultured under a free-living state. It is characterized by filamentous brown to olive in color culture, its vegetative cells are cylindrical and their diameters ranged from 8 to 9µm width and from 5 to 6 µm length. Heterocysts were found to be internal and terminal in the filament, its shape is spherical and its diameters ranged from 9 to 9.5 µm width and from 9 to 9.5 µm length. Akintes are present with cylindrical shape, with diameters of 9-10 µm width and 6-8 µm length. Nitrogenase activity of Anabaena azollae increased gradually from 0.1786 to 4.7992 μ mole C2H4 g soil/hr along 4 weeks. The strain showed high efficacy in suppressing the fungal mycelial growth of either Fusarium oxysporum or Alternaria alternate by 100 %.