Recently considerable concerns are increased for the health effects of extremely low frequency electromagnetic fields ELF EMFs, especially power lines frequency of 50-60 Hz. The need for complementary work to assess the health consequences that may be attributed to the exposure to such fields is a must. The present work is aimed to study the effects of 4kV/m -50 Hz electric fields EF on biomechanical and biochemical properties of rats' tibia bones. Similarly to occupational workers the assigned experimental animals were exposed 8 h/day for different exposure regimes of 5,10,15,20 and 30 days.At the end of the exposure periods, thetibia bone samplesare carefully collected, dissected free and cleaned of soft tissues. Effects of exposure on collected tibia samples from each group were obtained and monitored relative to un-exposed ones. Characteristic stress-strain curves were established at rate of 0.5 mm/min and biomechanical parameters were determined for all assigned tibia samples. Furthermore, all tibia samples were put in furnace to obtain bone ash and concentration of calcium, phosphorus and collagen were measured. The results obtained by overall biomechanical and biochemical parameters were significantly decreased and relatively changed by remarkable ratios as compared to unexposed ones. On conclusion, the present findings supporting the hazardous effect of exposure to ELF EFs and its effects are highly correlated to the exposure duration. In addition, bone is substantially sensitive organ for exposure to ELF EFs and may be losing its fine structure and its material form as long as it exposed.