THE EFFECTS of extremely low-frequency electromagnetic fields (ELF-EMFs) on the growth and synthesis of microcystins (MCs) production of the harmful cyanobacterium Chroococcus minutus were examined by exposing cyanobacterial cells to various ELF-EMF frequencies (0.1–1Hz) for various exposure times (10–60min). C. minutus cultures exposed to ELF-EMF at a frequency of 0.5Hz for 40min had significantly fewer cells than the control. Under these conditions, intracellular and extracellular (MCs) and chlorophyll-a concentrations also decreased significantly. Within 48h, no extracellular MCs were detected in cultures exposed to ELF-EMF for 60min. This study offers an eco-friendly technique for removing harmful cyanobacterial toxins from water resources. By degrading extracellular MCs after cell lysis, ELF-EMF is non-destructive, non-reactive and safe for the environment. In addition, it prevents additional aquatic environmental pollution input.