Six autopsy cases of Serratia meningoencephalitis were reported. The symptoms of this infection become apparent at an early stage in neonates; the meningoencephalitis in these six cases was severe, with or without inflammatory lesions in other organs. Serratia marcescens was originally described as a nonpathogenic organism; however, it is believed that after entering the blood stream of neonates, it becomes pathogenic, especially to the central nervous system. Meningoencephalitis due to Serratia marcescens is very severe and takes a rapid and progressive course against which no antibiotics have been found effective. Prevention of this infection is therefore considered of crucial importance.