To investigate age-related changes of GABAergic neurons and GABA expression in the cerebellar cortex of young adult and old cats,we applied Nissl staining to show the structure and neurons in cerebellar cortex.Immunohistochemical method was used to show the GABA immunoreactive neurons.Under light microscope,the numbers of total neurons and GABAergic neurons in the molecular layer,Purkinje layer and granular layer were counted respectively,and the average gray value of GABA immunoreactive neurons was measured with Image-Pro Express Software.The GABA immunoreactive cells,the fibers and their terminals were distributed in each layer of cerebellar cortex in young adult and old cats.Compared to young cats,the number of the neurons and GABA immunoreactive neurons declined significantly in the molecular and Purkinje layers of old cats(P<0.01).However,no difference was observed in the number of GABA immunoreactive neurons in the granular layer of young and old cats(P>0.05).In addition,the intensity of GABA immunoreactivity was visibly weaker in old cats than in young adults(P<0.01).Purkinje cells in old cats showed much less GABA immunoreactive dendrites than in young cats.An evident loss of GABAergic neurons and decline of GABA expression during aging may result in the functional degeneration of motor coordination,accurate timing and motor learning in old individuals.