This study was conducted at the laboratory of histology and anatomy, Faculty of Medical and Health Techniques/Kufa, and laboratory of post Graduate/ Department of biology, Faculty of Science/University of Kufa, The present study was conducted to investigate the effect of Prazosin hydrochloride on some organs in male rats (Rattus norvegicus), about 25 mature male rats with the average body weight of 210-290gram and three months age were randomly divided into four groups (5rats / group). The first group was given orally with distilled water as a control group and the other groups (second, third, and fourth) were also given orally with three doses of Prazosin (25, 50,75 mg /kg. b.wt.) daily for a period of eight weeks. At the end of the treatment period (eight weeks), rats were sacrificed, blood samples obtained, and organs lung, and spleen. The histopathological changes of lungs in the rats treated with prazosin at dose 25 mg/kg.b.wt for 8-weeks showed emphysema and dilation in some of the alveoli, hemorrhage distributed inside the tissue of the lung, polymorphic nuclear infiltration due to pneumonia, the pulmonary artery revealed degenerative changes in the tunica media structure (smooth muscle) and hyperplasia in the connective tissue around pulmonary artery and alveoli. These symptoms which occur in rats treated with prazosin at dose 50 and 75 mg/kg b.wt. as well as the histopathological changes of rat lung demonstrate severe hemorrhage, emphysema, thickening in the wall of some alveoli, pneumocyte necrosis (pneumocyte type 1 and pneumocyte type 2), and showed exudate among lung tissue. Histopathological changes of Spleen in the rats treated with prazosin at doses(50 and75)mg/kg b.w. for 8-weeks revealed histopathological changes, which represented by proliferation in the white pulp lead to fused white pulp together and destruction of some components of red pulp, stenosis in many splenic venous sinuses, the germinal artery show thickening in the tunica media and stenosis occurs, degenerative change in many nuclei of lymphocytes, and proliferation in the component of the white pulp.