Objective To probe into the relationship between the viral encephalitis and herpes viral infection, to understand the primary patheogeny of herpes viral encephalitis.Methods HSVⅠ-DNA,HSVⅡ-DNA,VZV-DNA,HCMV-DNA,EBV-DNA in CSF from viral encephalitis patients were detected by PCR.Results 82(15 6%) cases of 526 patiens with viral encephalitis were diagnosed as herpes simplex viral encephalitis, of which the age of high morbidity was at 0～10 years old children,9(1 7%) cases as cytomegaloviral encephalitis,7(1 7%) cases as varicella-zoster viral encephalitis and 4(0 7%) cases as EB viral encephalitis.Conclusions Herpes simplex viruses are the primary pathogeny in herpes viral encephalitis, PCR technique is valuable for the diagnosis of herpes viral encephalitis.