Objective To study the internal atlas sphincter of rats with congenital anorectal malformations(ARM)by observing the number of the ganglion cell and the number of nerve plexus in the internal sphincter.Methods Healthy pregnant Wistar- Imammichi rats are induced to ARM by ETU.67 rats with ARM were obtained.The pelvis was continuously cut from the exactly midsagittal plane, and the slices were stained with HE to observe the number of the ganglion cell and the number of nerve plexus in the internal sphincter under microscope.Result The average number of the ganglion cell in the rats with ARM was 1.206,and the number of the nerve pluxes is 0.310.The numbers in both two groups were extremely less than that in normal rats(P＜0.05).The rats without ARM which were also dealt with ETU had no distinctness compared with the normal rats.Conclusion The pathology changes of ARM includes many ways,for example,muscles,mucosa and the nerve system.The decrease of the ganglion cell and the nerve plexus in internal sphincter is an important aspect of ARM.