This study investigates the extremely low -frequency electromagnetic fields (0.1 -1Hz) on the growth of two species of toxic cyanobacteria with different habits including the colonial Microcystis aeruginosa and the filamentous Anabaena circinals, commonly found in drinking water sources. The results showed that Anabaena cultures exposed to ELF-EMF exhibited a sharp reduction in the cell numbers at frequency of 0.7, compared to control cultures. On the other hand, ELF-EMF had no significant effect on the growth of M. aeruginosa. The inhibitory effect of ELF-EMF on the growth of Anabaena increased with the increase in exposure time, with complete cell death obtained in 2-hour-exposed cultures. Moreover, ELF-EMF induced morphological changes in Anabaena cells and filaments. The study suggests further investigation of the effect of ELF-EMF for inactivation and inhibition of other toxic cyanobacterial species.