Abstract: This study was conducted to compare the effect of short duration high intensity and long duration low intensity progressive aerobic exercise on selected health related fitness components and hematological parameters on male students of Haramaya University. Subjects were randomly assigned to short duration high intensity and long duration low intensity groups. Both experimental groups participated in aerobic exercise 3 days/week for 12 weeks. The variables selected for the study were: cardiovascular endurance, muscular endurance, flexibility, body composition, WBC, RBC, hemoglobin and platelets. Throughout the training program, tests were taken at pre training, during training, post training. The results obtained in this study indicated that there were significant improvement in selected variables in both groups except BMI, hemoglobin and platelets under long duration low intensity group in which they showed insignificance (p < 0.05). According to this study when both groups compared, the short duration high intensity training program was significantly better than long duration low intensity training program in improving cardiovascular endurance, muscular endurance, flexibility, body composition, white blood cell, red blood cell, platelets and hemoglobin.