To investigate the cognitive role of the cerebellum of fish, we conducted experiments examining effects of cerebellar manipulations on fear-related classical heart rate conditioning in goldfish. We performed two types of manipulations, one was total ablation of the corpus cerebelli and the other was localized cooling of the corpus cerebelli for reversible inactivation of the cerebellar function. Both the cardiac arousal response to the first presentation of the conditioned stimulus and the cardiac reflex to the aversive unconditioned stimulus were not impaired by the ablation or cooling of the corpus cerebelli. On the other hand, inactivation of cerebellar function severely impaired the acquisition of a conditioned cardiac response in the fear-related conditioning. In addition, localized cooling of the corpus cerebelli reversibly suppressed the expression of established conditioned response. We suggest that the cerebellum of fish is not only being a motor coordination center but also is involved in emotional learning.