Under a magnetic field the activities of superoxide dismutase (SOD) in vitro and in vivo and accompanying activities of catalase activity in vivo were investigated in soybean roots. In plant cells a magnetic field creates a stress condition as other environmental stress factors do. To respond to the stress conditions, the occurred reactive oxygen species are scavenged by defense systems. In this study, two enzymes of the defense system, SOD and catalase activities were investigated under magnetic field. Enzyme and soybean seeds exposed to a magnetic field for a period of 2.2, 19.8. and 33s at the magnetic flux of 2.9-4.6 mT. SOD activities data were compared with magnetized enzyme and soybean roots. While the absorbance values of enzyme that passed through the magnetic field with a period of 19.8s for 24 hours were measured and SOD activity was significantly increased. At the same time, magnetic field SOD activity of the soybean roots was increased 21.18 % relative to control (P<0.05). After soybean seeds were treated by various magnetic fields and time periods, the activities of superoxide dismutase and catalase were significantly increased (P<0.05) during germination. At the 19.8s for 72 hours, SOD and catalase activities were increased 21.15% and 15.20% relative to control, respectively. Thus, it is indicated that the function of defense enzymes in seedlings was intensified due to the treatment of magnetic field. The increases of magnetic field exposure times do not cause linear increases in enzyme activities in vitro and in vivo studies.