Abstract: The study was to investigate the effects of simulated microgravity on bone marrow mesenchymal stem cells (BMSCs),including cell morphology,proliferation,cytoskeleton,cell adhesion,and the relationship between the activity of RhoA and those effects.RhoA activity was maintained by GST-CNF<i<γ</i< when BMSCs were cultured under simulated microgravity.The microfilament structure and vinchlin were detected via immunofluorescence staining.Western blot was used to detect RhoA and vinchlin expression.The results showed that the simulated microgravity could decrease the RhoA activity,change the cell morphology,microfilament structure,and the cell adhesion.CNF<i<γ</i< can maintain the activity of RhoA,and the above simulated microgravity effects can be partly reversed by CNF<i<γ</i<,suggesting that simulated microgravity may affect cytoskeleton,cell adhesion by inhibiting RhoA activity.