This study was conducted to investigate the effects of exercise on Bax/Bcl-2 ratio and Caspase-3 in dentate gyrus of hippocampus of socially isolated rats. For study, thirty two male Sprague-Dawley(SD) rats were divided into four groups: Group-housed/Control(GC: n=8); Group-housed/Exercise(GE: n=8); Isolated/Control(IC: n=8); Isolated/Exercise(IC: n=8). After environmental adaptation period for 2 weeks, rats were housed in isolated condition for 6weeks. And then, rats subjected to treadmill exercise were for 5days a week over 6weeks, and the speed was gradually increased (5m/min(5min), 8m/min(5min), 11m/min(20min)). After 24hours exercise sessions, rats were sacrificed. Significant increases of Bax/Bcl-2 ratio and Caspase-3 expression were observed in hippocampus of IC group, but significantly reversed in IE group. These results show that exercise may play crucial role to suppress pro-apoptotic responses in hippocampus of socially isolated rats.