Abstract. We have built a realistic computational model of the cerebellum. This model simulates the cerebellar cortex of the size 0.5mm×1mm consisting of several types of neurons, which are modeled as conductancebased leaky integrate-and-fire units with realistic values of parameters adopted from known anatomical and physiological data. We demonstrate that the recurrent inhibitory circuit composed of granule and Golgi cells can represent a time passage by population of active granule cells, which we call “the cerebellar internal clock”. We also demonstrate that our model can explain Pavlovian eyelid conditioning, in which the cerebellar internal clock plays an important role.