This study aims to mention the difference in VO2 max value in adolescents and the difference in leukocyte, monocytes, and neutrophil levels after 12 minutes of moderate aerobic exercise. The study was conducted using a cross-sectional study in 15 basketball players & 15 non-basketball students at SMAN 1 Banjarbaru. The sampling technique was carried out using purposive sampling method. Measurement of VO2 max value was carried out on the first day using the MFT (Multistage Fitness Test / Bleep Test) and measurement of leukocyte levels was carried out on the third day using blood collection after the patient did 12 minutes of moderate aerobic exercise. Data analysis used the Mann-Whitney test for VO2 max values & unpaired t test for the number of leucocytes, monocytes, neutrophils & cortisol levels. The results of the data analysis showed that there were still significant differences in the VO2 max value in basketball & non-basketball players (p> 0.05), monocytes (p> 0.05), & neutrophils (p> 0.05) and there were significant differences in levels. cortisol (p <0.01) after 12 minutes of moderate aerobic exercise in basketball and non-basketball students. The conclusion of this study is that 12 minutes of moderate aerobic exercise resulted in a higher increase in cortisol levels in basketball players compared to non-basketball players and the average value of leukocytes, monocytes, and neutrophils in basketball players was lower than non-basketball players. This is because the release of cortisol is a form of adaptation to the body's stress due to training, and becomes anti-inflammatory as a result reduces the number of leukocytes, monocytes and neutrophils of basketball players. 12 minutes of aerobic exercise can be used as a method to increase the body's immune system and explain the homeostasis process in adolescents in a good way.