A total number of 45 of Bovans laying hens at 42 weeks of age were randomly distributed into five experimental groups and treated with different levels of vitamins A; E and selenium to investigate their effects on some important tissues (ovary and spleen) of laying hens under heat stress conditions. Histopathological examination revealed that ovaries of birds received diet containing 500 mg/kg diet of vit. E with 0.25 mg/kg diet of selenium were moderately activated with an increase of primary oocytes. However, the spleen showed moderate hyperplasia of the white pulp and focal thickening of the splenic capsule. Birds fed on diet containing 8000 IU/kg diet of vit. A and 500 mg/kg diet of vit. E showed moderate activity of ovarian follicles with hypercellular stroma. The spleen showed hyperplasia in the lymphoid cells of white pulp and an increase in the reticuloendothelial cells (REC). Birds that received diet containing 16000 IU/kg diet of vit. A showed slight increase in the primary and growing ova as compared to control. The spleen revealed moderate hyperplasia in the white pulp area. Moreover, birds received diet containing 16000 IU/kg diet of vit. A, 500 mg/kg diet of vit. E and 0.50 mg/kg diet of selenium showed active ovaries containing variable sized ova and numerous blood capillaries. The spleen showed hyperplasia of the white pulp area.    It is concluded that the addition of vitamins A; E and Se to layer diets activated the ovarian function and enhanced the immune response of laying hens under heat stress conditions.