One of the important changes of sport and physical activity in human beings is hormonal changes; these changes have different effects based on intensity, duration and type of training. Beta endorphin (BE), one of the neural system hormones, shows changes in blood plasma level by exercise. This neuropeptide plays an important role in pain relieving, well-being, mood enhancing and euphoria. The aim of this research was to compare the effect of one session of aerobic and anaerobic training on plasma beta endorphin changes in active and sedentary girls. After distributing the physical activity questionnaire in Alzahra University, 12 physical education students as active group and 12 non-physical education students as sedentary group were selected. Bruce and Rast tests as aerobic and aerobic tests were applied. Beta-endorphin concentration was determined before and after the tests. t test and ANCOVA were used to analyze data. The results showed that plasma BE level increased in both active and sedentary groups after aerobic training. Also, BE level increased after anaerobic training in both groups. No significant difference was observed in BE between the two groups after both aerobic and anaerobic training. No difference was observed between aerobic and anaerobic training in subjects. No difference was observed in both types of training between the two groups.