Abstract: Recent development of the medical imaging is the changing from macro-imaging to the micro-imaging by improving the spatial resolution and the contrast resolution of the soft tissues. Cells and microstructure of ím magnitude can be visualized in vivo non-invasively and dynamically by medical micro-imaging technique. Medical micro-imaging is capable of making the pathological diagnosis more early and the treatment of the leision more precisely by ã knife. Because the phase contrast resolution of X ray in soft tissues is about one thousand times higher than that of the absorption X ray method, so the phase contrast imaging is becoming the hot spot of the medical imaging. In this paper, the synchrotron X ray source at BSRF was used to investigate the microstructure of lung, liver and kidney by means of the DEI phase contrast micro-imaging method.Resultsindicated that the microstructures of lung alveoli, renal tubulous, liver lobules etc, which could not be seen by conventional absorption X ray method but could be revealed clearly by phase contrast imaging method. The spatial resolution reached about 20 ím. It is concluded that the medical phase contrast micro-CT is a new developing technique of the medical imaging in the near future.