Objective To investigate the effects of simulated weightlessness on cell area,cell multiplication and cell cycle of MG-63 cells.Methods The rotating clinostat was used to simulated weightlessness.The change of cell area was measured with image processing and analysis soft(Image J).Cell growth curve was measured with the cytometry.The change of cell cycle was examined with a flow cytometer.Results Compared with control group,the cell area of cell line MG-63 in 24 h,36 h and 48 h duratons of rotating group decreased significantly(P0.05).Compared with 12 h duration,the cell area in 24 h,36 h and 48 h durations of rotating group decreased significantly(P0.05).But in control group,cell area of all 4 experimental durations showed no significant difference among each other.Compared with control group,cell growth curve revealed that cell multiplication was inhibited in rotating group.Compared with control group,the cell cycles of cell line MG-63 in 12 h,36 h,48 h sections of rotating group did not change significantly,but the cell in 24 h duration of rotating group was decreased significantly(P0.05) in G0+G1 phase and increased significantly(P0.05) in S phase.Conclusion Simulated weightlessness in rotating clinostat may lead cell area of cell line MG-63 in 24 h,36 h and 48 h durations to be decreased.The cell multiplication is inhibited in 12 h,24 h,36 h and 48 h durations.The conversion of cell from S phase to G2 phase is inhibited in 24 h duration.