Abstract: This paper focus on the extraction and pretreatment of forensic specimens. The experimental studies on tissue distribution of phosacetim and effects of storage conditions on phosacetim concentration showed that liver was very useful in forensic analysis for its higher phosacetim level,which was little affected by the storage time and temperature.Extraction methods of biological sample had also been investigated and the results indicated that the use of enzymic digestion of liver tissue in the determination of phosace- tim was no more effective than modified direct extraction method,which was quick and easy operation and its recovery rate was about 80％.