Aging is a complex biological process characterized by the accumulation of changes over time with loss of physiological integrity. Age-related changes occur in all tissues of the body and affect the functioning of all body systems. The purpose of this study is to investigate the effect of aging on male reproductive function, different body fat and skeletal muscles weight, and hematological parameters in male Sprague–Dawley rats. 50 male rats were randomly divided into two groups (n= 25/group): young and old groups. The rat in the old group was reared for 12 months. Changes in body weight were monitored weekly. The results showed that body mass index (BMI), mean abdominal circumference and testes, epididymis, seminal vesicle, and prostate weights were increased in the old group. Additionally, pre-renal, epidydimal, inguinal fat, and brown adipose tissue (BAT) weights were enlarged in the aged group. Weights of gastrocnemius, soleus, and extensor digitrum longus (EDL) muscle were also significantly increased in old rats. The blood glucose and corticosterone levels were significantly declined by age. Erythrocytes count (RBCs), hemoglobin concentration (Hb), the percentage of packed cell volume (PCV), and mean corpuscular hemoglobin concentration (MCHC) were decreased while the mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) were increased with aging. Both sperm cell concentration and sperm abnormalities were increased while sperm motility decreased in the old group. In conclusion, Aging has adverse effects on some hematological and reproductive parameters in male rats. Therefore age is a fundamental factor that should be carefully considered.