Lower body negative pressure (LBNP) and cycle ergometer have been used in space flight as effective countermeasures in several years. But the physiological effects of their combination on preventing the muscle atrophy induced by microgravity or simulated microgravity have been less reported, especially in women. This study was to investigate the effects of combined LBNP and ergometer on preventing the muscle atrophy induced by 15-day bed rest in women. Method: 22 healthy female subjects were assigned to 1) group A (no exercise counter-measure, control group, n = 8), 2) group B (LBNP exercise group, n = 7) and 3) group C (LBNP + ergometer exercise group, n = 7). They all experienced the bed rest with 6° head-down tilt position for 15 days. At the end of bed rest, the subjects were examined the peak torque of knee joint for muscle strength, DEXA examination for lean mass of lower body, and MRI for muscle volume (quadriceps femoris, gastrocnemius and soleus). Results: The muscle strength, lean mass of lower body and muscle volume were significant decreased after 15-day bed rest (P<;0.05). The decrement of muscle strength, mass and volume was less in LBNP exercise group and the combined exercise group, the maximum decrement happened in control group. Conclusion: There were a few benefits from combined exercise to prevent the muscle atrophy induced by 15-day bed rest, but its effect of sustaining the muscle function was almost same as LBNP exercise alone. Considering its advantage in enhancing aerobic capacity (paper in press), the combined LBNP and ergometer exercise has the potential to be an effective countermeasure which could be used in space flight for female astronaut.