Objective To analyze the excision of accessory navicular with reconstruction of posterior tibial tendon insertion on navicular for the treatment of flatfoot related with accessory navicular and to evaluate its effectiveness. Methods Between May 2006 and June 2011, 33 patients (40 feet) with flatfoot related with accessory navicular were treated. There were 14 males (17 feet) and 19 females (23 feet) with an average age of 30.1 years (range, 16-56 years). All patients had bilateral accessory navicular; 26 had unilateral flatfoot and 7 had bilateral flatfeet. The disease duration ranged from 7 months to 9 years (median, 24 months). The American Orthopaedic Foot and Ankle Society (AOFAS) ankle-midfoot score was 47.9 ± 7.3. The X-ray films showed type II accessory navicular, the arch height loss, and heel valgus in all patients. All of them received excision of accessory navicular and reconstruction of posterior tibial tendon insertion on navicular with anchor. Results All patients got primary wound heal ing without any compl ication. Thirty patients (36 feet) were followed up 6-54 months with an average of 23 months. All patients achieved complete pain rel ief at 6 months after surgery and hadgood appearance of the feet. The AOFAS ankle-midfoot score was 90.4 ± 2.0 at last follow-up, showing significant difference when compared with preoperative score (t=29.73, P=0.00). X-ray films showed that no screw loosening or breakage was observed. There were significant differences in the arch height, calcaneus incl ination angle, talocalcaneal angle, and talar-first metatarsal angle between pre-operation and last follow-up (P lt; 0.01). Conclusion The excision of accessory navicular with reconstruction of posterior tibial tendon insertion on navicular is a good choice for the treatment of flatfoot related with accessory navicular, with correction of deformity, excellent effectiveness, and less complications.