Abstract: Extracting DNA from faecal sample is a newly developed technology of recent years. Although several methods to extract DNA from faeces have been developed home and abroad, they addressed fresh samples and it is still blank in extracting DNA from old faeces yet. Extracting old faeces' DNA can make the full use of transfers out or the death animal's genetic information and expanding the application scope of Molecular Scatology. In this experiment two groups of faeces were launched into DNA extracting. One group had been preserved by absolute ethanol for 3 years and the other group had been preserved by absolute ethanol for half past 4 years. Aiming at the old faecal's characteristic of small number of cells and high degrading of DNA, several repetitions(4 tubes) were carried out at the same time in this experiment. Then 4 different DNA extracting methods (Preprocess-phenol/chloroform extraction method, Guanidine thiocyanate method, CTAB method, QIAamp DNA Stool Mini Kit, Qiagen) were followed. From these parallel methods and their corresponding results, we could get the best method while the possibility of extracting DNA from old faecal was studied. After DNA was dissolved in TE we got the original DNA. Finally we collected the original DNA from the 4 repetitions then purified and concentrated it by using DNA purification kit. In the end, the results of PCR amplification shows that only Preprocess-phenol/chloroform extraction method can extract enough DNA for PCR from two groups of faeces. In our study, we extracted DNA from old faeces successfully and got some genetic information from mtDNA. This result confirms the possibility of putting old faecal into molecular scatology study.

Key words: DNA extracting, Old faecal, Preservation, PCR amplification