The present book has been undertaken to evaluate the biological changes that could be encountered in response to extremely low frequency magnetic field (0.85 mT). The effect of magnetic field on oxidative stress (reduced glutathione and total lipid peroxide), hematological indices, total and differential leukocytic counts, cardiac functions (creatinine phsphokinase and lactate dehydrogenase), level of calcium ions concentrations and total proteins content, have been investigated in this work. The present book has been conducted on the effect of magnetic field for 7 days (2 hours/day) in the case of exposure. Blood samples were obtained from the rats before and after 2,4,6,8,10,12, and 14 hours post-exposure to the magnetic field.Blood was used for the determination of hematological indices, total and differential leukocytic counts and reduced glutathione content (GSH). However, serum samples were used for the determination of the level of total lipid peroxide, activities of creatinine phosphokinase (CPK) and lactate dehydrogenase (LDH), calcium ions concentration and total proteins content. The statistical analysis was done using unpaired t-test (p< 0.05).