Objective To evaluate the effects of selective brain hypothermia on the expression of miR-484 during cerebral ischemia-reperfusion ( I/R) in rats. Methods A total of 120 clean-grade healthy male Sprague-Dawley rats, aged 8-10 weeks, weighing 250-300 g, were divided into 4 groups ( n=30 each) using a random number table method: sham operation group ( group S) , cerebral I/R group ( group I/R) , hypothermia group ( group H) and normothermia group ( group N) . Blood vessels were only separa-ted and ligated without blockade in group S. In the other three groups, cerebral I/R was induced by inser-ting a nylon thread with rounded tip into the right internal carotid artery, and the middle cerebral artery was occluded for 2 h followed by reperfusion. In group H, 4℃ normal saline was infused for 15 min at a rate of 80 ml·kg-1 ·h-1 through the internal carotid artery immediately after removing the nylon thread. In group N, 37 ℃ normal saline was infused in the same way. Neurological deficit scores were evaluated at 6, 24 and 48 h after reperfusion. Animals were then sacrificed, the cerebral cortex of the ischemic penumbra was removed for determination of nerve cell apoptosis ( by TUNEL method) , expression of mitochondrial fission protein 1 ( Fis1) ( by Western blot) and expression of miR-484 ( quantitative real-time polymerase chain re-action) . The apoptotic rate was calculated. Results Compared with group S, the neurological deficit score and apoptotic rate of nerve cells were significantly increased, and the expression of Fis1 was up-regulated at each time point in the other three groups, the expression of miR-484 was significantly down-regulated in I/R and N groups, and the expression of miR-484 was significantly up-regulated in group H ( P＜0. 05 or 0. 01) . Compared with group I/R and group N, the neurological deficit score and apoptotic rate of nerve cells were significantly decreased, and the expression of Fis1 was down-regulated, and the expression of miR-484 was up-regulated at each time point in group H ( P＜0. 05 or 0. 01) . Conclusion The mechanism by which se-lective cerebral hypothermia attenuates cerebral I/R injury is associated with up-regulating miR-484 expres-sion and thus down-regulating Fis1 expression in rats.