The effects of the exposure to Dynamic magnetic field (ACMF) of 7,10 and 15 gauss for periods from 4 to 12 hours on the Sclerotium cepivorum were studied in vitro by using microscope (Leica version 1.8, Germany). ACMF made changes in the thickness of the mycelium of the fungus and reduce the production of sclerotia . Data was indicated there is no significant between the three media with average 44.03, 44.38 and 45.00 respectively. Also, there is no significant between the periods of exposure (4, 12 h) with average 41.44, 47.50. the interaction between Media x Hours (M x H) show there are significant difference between them. Finally, I conclude that by increase the period of exposure time of Dynamic magnetic, it will decrease the Disease severity and the Disease incidence.