Pseudoaneurysm is one of the complications of arterial injuries by trauma. The case report in children is rare, although not in adult. A 7-year and 10-month girl was visited with the complaints of pain and a mass in her right leg. At first, the radiograph of right tibia showed a remarkable cortical erosion from without, suggesting mass effect by a soft tissue tumor. She had a history of fracture of right tibia, and then manipulative reduction and K-wire fixation at 11 months ago. Arteriography showed a formation of the pseudoaneurysm originated from the posterior tibial artery. The operation was done through the ligation of artery at proximal and distal to pseudoaneurysm, and then excision of mass. At 5 year follow-up, the configuration and function of right foot was normal. Eventually, the cause of the mass formation is thought by the trauma of fracture fragment at the time of accidents, but the possibility of penetrated injuries by K-wire should be ruled out, which is used frequently in children's fracture. We experienced a case of traumatic pseudoaneurysm of posterior tibal artery with tibial fracture, especially occurred in pediatric patient, and presented the result of long-term follow-up.