To develop the method for separation of epithelial cells and sperm in a microfludic chip,the glass-PDMS chip,which is easy to manufacture,was selected to separation of epithelial cells and sperm.Buffer was added to the inlet(7μl)and outlet reservoirs(10μl)prior to sample addition,then epithelial cells/sperm mixture(2μl)was added to the inlet reservoir.After a minimum of 8 min of “settling time”,gravity-induced flow was initiated by removing 3μl of buffer from the outlet reservoir,then the inlet reservoirs was supplemented with 1μl buffer every 5 min.Following the desired separation time,product was removed from the outlet reservoir via pipet.Nulease was used to remove free DNA,followed by extraction,amplification and electrophoretic separation/detection.By using microfabricated chip based gravity-induced fiow mechanisum,sperm can be separated from mixture in 30 min,No epithelial cells were observed passing through the channel during separation.After removing free DNA by using nuclease,a single and complete sperm STR profile can be obtained.Compared with conventional differential extraction,this method can largely save test and has a certain value for the analysis of forensic evidence in sexual assault cases.