Pathological characterizations of the central nervous system (CNS) of dogs with acute canine distemper were the demyelination in white matter and the formation of inclusion body in astrocytes. In order to further observe the features of primary brain lesions and inclusion body induced by Canine distemper virus (CDV) and investigate the reliant clinical neurological signs on brain lesions 10 dogs with acute canine distemper were detected in detail. To detect the lesions carefully the brain tissue was divided into three portions and eleven slices, that is cerebrum (five slices), cerebral stem (four slices) and cerebellum (two slices) according to anatomical location; stained with hematoxylin and eosin (HE), luxol fast blue (LFB) and Immunohistochemical assay. The results revealed that the specific demyelination and mild lesions was widespread in cerebra tissue and severe demyelination was encircling or near the third ventricle in the brain stem. Base on mild or moderate diffuse demyelination the severe multifoci lesions occurred in cerebella. In the demyelinating areas vacuolation and spongy appearance were obvious, glial cells were a few and no inflammatory reactions were displayed. The demyelinating lesions were non-symmetric appearance and no special affinity for particular traces. The more eosinophilic intracytoplasmic and intranuclear inclusion bodies were found in ependymal cells of lateral and the third ventricle and astrocytes that were often near the ventricles. With anti-CDV antigen assay, the ependymal cells with inclusion bodies showed an intensive positive reaction. Some of pyramidal cells, nervous nucleus cells and Purkinje cells were degeneration and cytolysis, or shrunken with pyknotic nucleus,especially in small pyramidal cells. According to this experiment it was considered that the primary brain lesions induced by CDV were a demyelinating encephalopathy, but not encephalitis. The inclusion bodies located in ependymal cells were a important evidence for determination of canine distemper in brain tissues. The brain lesions induced by CDV were non-specific injury about neuron and nervous nuclei, so that manifested the different neutrological signs.