The purpose of this study is to examine the serum BDNF, Epinephrine, Norepinephrine and working memory of the adolescents who are still undergoing brain development when the intensity of their aerobic exercises differs. The subjects of this study are 30 students with no history of physical illness from D middle school which is located in Gyeonggi do Republic of Korea. The groups were divided into low intensity exercise group, middle intensity exercise group and control group. The homogeneity among the groups were verified. The exercises were performed 3 times per week in the duration of 12 weeks using treadmills. The Aerobic exercises were designed to burn 200kcal and the exercise time for each group was calculated for the consumption of 200kcal and the exercises were applied to each individual for the duration of 12 weeks. Before and after 12 weeks of aerobic exercises of different levels, the middle intensity exercise group showed a significant increase in BDNF when at rest (p<.05) but low intensity exercise group and control group was showed no significant. Epinephrine, Norepinephrine was showed no significant. Before and after 12 weeks of aerobic exercises of different levels, the middle and low intensity group level exercise group showed a significant increase in working-memory(p<.05)