Abstract: Abstract: 20(s)-protopanaxadiol is labeled with 2H and 3H, respectively. UV absorption spectrum and Rf of tritium labeled 20(s)-protopanaxadiol are the same as authentic sample. The radiochemical purity of 3H-aPPD is more than 95%, and the specific radioactivity is 1.57×108GBq/g. To study the character of aPPD on human lung cancer A549 cell line, the specific radioactivity of cytoplasm and nucleus are detected. It was shew that aPPD reached maximum concentration after 24h both in cytoplasm and nucleus. The results provide the direct evidence that aPPD, which structure looks like the steroid, can enter the nucleus to play its pharmacological effects. The present study can be served as the base for the further studies of its mechanisms.