Background: Flat feet or pes planus is a complex disorder with a diversity of symptoms and varying degrees of deformity that is caused by structural loading changes along the medial part of the feet and plantar arches, when the arch starts collapsing, balance is disturbed at the feet, and therefore the balance throughout the entire body is also disturbed. Purpose: to investigate the effect of foot insole and biodex balance training on dynamic balance, risk of fall, and functional ankle instability in flexible flat feet. Methods: Sixty subjects of both sex with ages ranging from 18-21 years and BMI ranging from 18-25 kg/m² with bilateral flexible flat feet participated in this study. They were assigned randomly and equally to two groups: group A and group B. group A received biodex balance training 3 sessions per week for 4 Weeks and short feet exercise 3 min each day for 4 weeks, each repetition was held for 5 sec and repeated for up to 3 min approximately 30 repetitions, 45-second rest period after each 10-repetition. Group B received same as group A and worn foot insole 6-8h per day. Overall stability index “OSI”, anteroposterior stability index “AP-SI”, and mediolateral stability index “ML-SI” were measured pre and post-treatment by Biodex Balance System at level 4. Cumberland Ankle Instability Tool was used to measure functional ankle instability “FAI”. Results: There was a statistically significant difference in post-study mean values of OASI (P=0.020), MLSI (P=0.012), APSI (P=0.020), and FAI (P=0.001) between the two groups in favor of group B. Conclusion: Foot insole combined with biodex balance training and short foot exercise are an effective method of treatment for dynamic balance impairment, risk of fall and functional ankle instability in flexible flat feet.