Abstract: The growth and development of more than 500 corn seeds flown on Long Duration EXposure Facility(LDEF),which 69 months in low-Earth orbit, were studied.The results of investigation indicated that the envionmental condition in spaee had no obvious effects on seed germination.Most of the germinated seeds from LDEF fight grew into plants normally,but with average height shorter than that of control.Variations,including White-yellow stripes on leaves,dwarfing,change of leaf sheath color or plant col-or,were observed in plants developed from these seeds.When the ferquency of white-yellow stripe formation was used as the endpoint and compared with data from ground based studies,the dose to which corn seeds might be exposed during this flight was estimated to be equiv alent to 635 cGy of gamma rays.Seeds from different holdere gave significant differentvariation frequency. White-yellow stripes on leaves were also found in some of the inbred progenies from plants displayed variation,Electron microscopy studies showed that the damage of chroloplast development in the white-yellow stripes on leaves was Similar between seeds flown on LDEF and that irradiated by accelerated heavy ions on ground.