The experimental results in effect of limb lengthening using metaphyseal osteotomy at proximal tibia on epiphyseal growth plate in 28 young sheep were reported. Radiographic, microscopic and electronmicroscopic findings showed that lengthening of 7.5% the growth plate resulted in narrowing in varying degrees in one third of the sheep with a lengthening rate of 0.25 mm every six hours. Narrowing of epiphyseal growth plate was seen in half of sheep with lengthening of 10% and in all sheep with lengthening of 12.5% and 15%. Degeneration and necrosis of chondrocytes happened in one sheep of lengthening of 15%. Thickening of growth plate was seen in all sheep of the control group. Our conclusion from this series of experimental studies was that depression caused by compression stress effect in limb lengthening of less than 7.5% on epiphyseal growth plate is minimal.