Microgravity(MG)effect is a weightlessness phenomenon caused by the distance from the ground or low gravity of other planets outside the earth's atmosphere.The various effects of MG have been corroborated in human and animal studies and modeled in cell-based analogs.However,the impact of MG on siRNA performance remains to be elucidated,which is crucial for aerospace medicine.In this study,we prepared nucleic acid nanomicelles(EAASc/siRNA)by using tri-block copolymer of PEG45-PAMA40-P(C7A36-DBA37)(EAASc)and siRNA and explored its working mechanism under simulated microgravity(SMG)condition generated by a random positioning machine(RPM).The binding ability of EAASc to siRNA and silence activity were firstly confirmed in normal gravity(NG)environment.Evaluation of PLK1 mRNA expression revealed that gene inhibition efficiencies were increased by 28.7％(HepG2)and 28.9％(A549)under SMG condition,compared with those under NG condition.In addition,mechanism exploration indicated that morphology and migration capability of cancer cells were significantly changed,the internalization of EAASc/siRNA by cells was magnified when the cells were incubated with RPM.No significant difference was observed regarding the expression profiles of genes involved in RNA interference(RNAi)pathway,including Ago2,Dicer,TRBP,and so on.Taken together,siRNA activity was elevated under SMG condition owning to increased cellular internalization.This study,for the first time to our knowledge,provides valuable theory for development and appli-cation of siRNA therapeutic in space in the future.