Objective To investigate the pathological evaluation method of intrathalamic neurovirulence test of poliomyelitis vaccine in monkeys. Methods Two hundred and forty healthy rhesus monkeys age 1-3 years, body weight 1.7-4.5 kg, in 12 lots, were used in this study. The monkeys were injected with poliomyelitis vaccine into bilateral thalamus. The animals were sacrificed after observation for 21 days and specimens of the brain and spinal cord were collected. After dehydration, embedding and sectioning, HE and gallocyanin staining were used for pathological observation. The pathological changes were scored, and the severity of the pathological changes were determined by scoring. Results The sections were taken from bilateral cerebellum (needle tracts included), midbrain, pons, medulla oblongata, cervical enlargement and the lumbar enlargement. The pathological changes were evaluated referring to the hemisection scoring method of intraspinal neurovirulence test. Lesions on both sides of the brain stem, cervical enlargement and lumbar enlargement were scored, and the severity of the lesions at these three regions were determined according to the average score. The total incidence rate of specific neuronal pathological changes was 15%. The incidence rates of lesions caused by different types of vaccines were similar. Most of the lesions were minimal, and severe lesions were seen mainly in the type III vaccine tests. Conclusions In intrathalamic neurovirulence test, scoring of the lesions of nervous system by hemisections can objectively reflect the pathological changes in the nervous system. This method is simple and easy to apply, practical, and can facilitate the unification of diagnostic criteria. We would recommend this method to be used in pathological evaluation in intrathalamic neurovirulence test of poliomyelitis vaccine.