Estimation of postmortem interval (PMI) is one of the difficult problems in forensic medicine. With the development of molecular biological techniques, DNA quantification methods were widely applied in estimating PMI. The postmortem degradation of DNA in different tissues and organs was discussed in this article and the recent DNA quantitative techniques being used for estimating PMI were reviewed. These techniques included single cell gel electrophoresis, Feulgen staining image analysis, flow cytometry.