The purpose of this study was to examine the effect of aerobic exercise on improving health related physical fitness components of Dembecha senior secondary and preparatory school grade 12 male students. The Purposive sampling technique was used to select 25 students were participants recruited as study subject from Dembecha senior secondary and preparatory school. These 25 students were assigned as one quasi experimental design and their age range were between 18-20 year .All selected subjects participated in low to moderate intensity aerobic exercise for 12 weeks (3month), 3 days per week and 60 minute duration at 55-70 maximum heart rate (MHR) per day from November 2019-January 2020. Pretest, during training test and post training test were conducted on selected variables of health related physical fitness components. The collected data was analyzed by paired sample t-test (SPSS v.20) to determine the mean differences value and to make comparison in between pretest and posttest mean value results. The level of significant was 0.05. According to analyzed data in step test was 17.64 beat per minute (p<0.01) mean difference were observed. the mean difference value boosted in 2.6km run test performance by 3.1744 minute P<0.001) after 12 week aerobic exercise training. In sit and reach test 7.280 cm (p<0.01) increment were observed respectively. But in body mass index 2.04000kg/m2 (p<0.01) decrement were observed throughout the study period. the result obtained in this study indicated that there were significant improvement in cardio vascular endurance, flexibility and there were reduction on body composition .Based on this finding, it can be concluded that 12 week low to moderate aerobic exercise have positive effect on improvement of HRPF components of Dembecha senior secondary and preparatory school grade 12 male students. Key Words: