Background: Ankle sprains are the most common musculoskeletal injuries that occur in athletes all over the world. Ankle sprains can also cause longterm disability such as Ankle pain, Functional Ankle instability, postural disorders, recurrent Ankle sprain and etc.Methods: The purpose of this study was to examine prospectively intrinsic and extrinsic risk factors for Ankle sprains in 125 Irainin athletes that were divided into two groups: Healthy and Injured groups. Ankle range of motions, Achilles Tendon’s flexibility and Calf’s size were measured and related questionnaire was completed.Results: Ankle sprains were more common in soccer, basketball and volleyball than other sports. Severe Ankle inversion was the most common (94.4%) mechanism of Ankle sprain. Fatigue, not warming up, improper landing, Ankle rotations were expressed by the athletes as the main reasons causing their Ankle sprains. There were no significant differences between ages, weight, height, training sessions, playing surfaces, foot wears and Ankle sprains. Most interestingly was the significant relation between balance training and Ankle sprain prevention (P value=0.00574).Conclusion: The intrinsic factors such as fatigue, not warming up, improper landing were most common risk factors for Ankle sprain in Iranian athletes. One of the main findings of the present study was the positive role of balance training as a key factor in prevention of Ankle sprains.