Introduction: The effect of aerobic exercise on the blood coagulation system as a risk factor for coronary disease is still controversial. This study aimed to investigate the effect of a session of moderate aerobic exercise on some of the blood coagulation factors in the young girls. Materials and Methods: This interventional study was conducted on 11 healthy female volunteers aged 21 to 24 years, who had taken no systematic physical exercise for one year. This study was approved by the Ethics Committee of Kerman University of Medical Sciences. The performed protocol comprised 30 minutes of running with 70-75% intensity of maximal heart rate reserved. Every volunteer donated blood for 3 times (before, immediately after and 30 minutes after the intervention), and the coagulation factors of Platelet count, Mean Platelet Volume, PT, aPTT, Fibrinogen and Factor VIII of plasma were measured. The data were analyzed using the repeated measures ANOVA. Results: Immediately after a session of aerobic exercise, the platelet count and factor VIII increased about 23% (P= 0.001) and 75% (P=0.004), respectively while aPTT decreased about 8% (P= 0.007). PT showed a delayed increase observed 30 minutes after the exercise (P< 0.001). Conclusion: The results revealed that physical exercise, even with moderate intensity, activates some of blood coagulation markers and can lead to further side effects and probably a longer recovery. These findings would be helpful in adjusting the exercise intensity for the sedentary people, especially at the beginning of the training course.