Exercise may play a role in the prevention of bone fractures in postmenopausal osteoporosis. The effects of endurance exercise on bone properties were assessed in 9-month-old sham-operated (SH) and ovariectomized (OVX) rats. The rats were either kept sedentary (SED) or were exercised (EX) on a rodent treadmill at 21 m/minute, 7% grade, 40 minutes/day, 4 days/week for 3 months. Bone mineral (by ash weight), morphometry, and biomechanical properties (by three-point bending) were evaluated after excision of bones at sacrifice. Ovariectomy resulted in a loss of bone mineral in femur, tibia, and fourth lumbar vertebra (L4), but biomechanical (force, deformation, stress, strain, and modulus of elasticity) and morphometric (length, cortical and medullary area, and moment of inertia) properties of femur were maintained. The ash weight of femur and tibia, but not L4, as well as femur yield and maximum force and moment of inertia, were improved in OVX-EX rats compared to OVX-SED animals. In SH rats exercise had no influence on ash weight of any of the three bones or femur morphometric properties, yet femur maximum force and plastic deformation were significantly enhanced compared to SH-SED rats. The results of the present study suggest that endurance exercise has beneficial effects on the bone mineral as well as biomechanical properties (femur yield and maximum force) during early stages after ovariectomy and improves the bending strength of the intact femur without an effect on bone mineral in sham-operated rats.