The stressful conditions including heat stress negatively affect to the animal’s reproductive performance. Apoptosis of granulosa cells under unexpected stimuli can influence the fate of ovarian follicles and its function. Since the changes in caspase-3, a key executioner of the apoptosis pathway, have not yet been elucidated in heat-stressed sows, this study compared its changes in the ovaries of domestic sows affected by heat stress during summer. The samples were collected at spring (23.1℃; CON group) as suitable temperature for raising pigs or at summer (34.4℃; HS group) as unavoidable chronic heat stress. It was not significant but strong tendency to release higher level of stress hormone (corticosterone) in HS group than that in CON group was identified. A significant upregulation of cleaved (activated) caspase-3 expression in HS group was identified compared to CON group, indicating that apoptosis was increased in the ovarian follicles during summer. The expression of cleaved caspase-3 in the ovaries was positively related with degree of maximal atmospheric temperature and serum levels of corticosterone. The caspase-3-positive cells were more prevalent in mature follicles with localization primarily in the granulosa cell layer than immature follicles. The intensities of c...