Abstract:Objective:To substantiate the effect of space co nditions on medicinal plants.Method:The seeds of platycodon grandiflorumg we re set up in retrievable satellites. After returning to earth, the ultrastructural changes of leaves were studied. Result: Under light microscope, the leaf tissue structure of the flig ht group and the earth controlled group were alike and under electron microscope , some differences could be found in the nucleus and choloroplasts between the t wo groups.Conclusion: Space environment has some effect on Platycodon grandiflorum, and the effect needs to be further explored.