The aim of this research was to study the effect of eight weeks of selected aerobic exercises on depression and serum serotonin concentration in depressed female university students aged between 18 and 25 in Aligudarz city. For this purpose, using Beck depression questionnaire, 20 female students with moderate depression were selected in two groups (experimental n = 10 and control n=10). To evaluate the impact aerobics Selected the concentration of serotonin in plasma, In order to investigate the effect of selected aerobic exercise on the concentration of plasma serotonin, the experimental group performed aerobic running for eight weeks (3 sessions per week) with 60-65% HRmax. The research variables were measured 24 hours before the first and 96 hours after the last session. The student t test and ANOVA were used to analyze data at P<0.05. Results showed that plasma serotonin level increased 50% in the experimental group although this increase was not statistically significant. Depression significantly decreased in experimental group compared to control group. Also, there was a significant relationship between increased serotonin and decreased depression. It can be concluded that selected aerobic exercise significantly decreased depression and increased concentrations of serotonin and proper physical activity can effectively treat depression.