There is critical need to do a lot of experimental studies to calculate of the relative biological effects of non-ionizing radiation and comparing its effect with ionizing radiation to re-determine the safe exposure dose to non-ionizing radiation. This research concerning to study the relative fraction of damage (RFD) of the extremely low frequency magnetic fields (4kV/m -50 Hz) to high energy photons (6 MeV) on some biophysical properties of rats bone. In this regards, 100 male albino rats are used and divided into sub groups 10 rats per each group. One group of animals was used as control group (unexposed group) and did not receive any treatment. Similar to occupational workers four groups of animals exposed 8h/day for periods from 1 to 4 weeks and immediately at the end of the exposure period are sacrificed. Four groups of animals exposed 8h/day for periods from 1 to 4 weeks and remained 45 days post exposure periods then sacrificed. The last group of animals was exposed to high energy photons 6MeV of dose (1rad). Femur bone samples of each animal from all groups are collected and prepared for further biophysical investigations. In addition, RFD of magnetic fields exposures are calculated for each group relative to dose of 6MeV-1 rad photons. Results of exposure to electric field showed significant deterioration affect overall biomechanical parameters of femurs as a consequential defect of bone strength and bone quality as compared to unexposed ones.