The present work is to study the relationship between DNA degradation in tissue cells and estimation of postmortem interval, and to provide a new way for the estimation of postmortem interval(PMI). The tissue cells of kidney and liver in vitro obtained at different time points were kept in a controlled environment. The kidney tissue and liver tissue were taken out every 4 h， during 48-72 h after death at 25 ℃. The DNA content in different tissue cells was examined by means of confocal Raman micro spectroscopy with an excitation wavelength of 532 nm. Results show that the relative peak intensities (I1 094/I2 923) of confocal Raman microscopy for the tissue cells decreased gradually with the prolongation of postmortem interval from 48 to 72 h after death, while the peak intensity at 1 094 cm-1 was reduced obviously; and the peak intensity at 1 454 and 2 923 cm-1 did not change significantly. It is concluded that the DNA content in tissue cells decreased gradually with the prolongation of postmortem interval from 48 to 72 h after death. There is a linear relationship between the degradation rate of DNA in the tissue cells and postmortem interval. This investigation shows that Raman micro spectroscopy is useful to the estimation of postmortem interval (PMI)．