The posterior tibial muscle is considered a plantar flexor as well as an invertor of the foot, which acts as a key muscle to the medial longitudinal arch by locking the talar joints in normal gait. Rupture of the posterior tibial tendon can cause a valgus deformity of the hindfoot and an abduction deformity of the forefoot which produces a typical flat foot and a talar dislocation in severe cases. The tendon of posterior tibial muscle can be ruptured spontaneously after the age of 40 from chronic stress at the ankle joint, or by sports injury and trauma. Severe foot deformity which can be prevented by early diagnosis and appropriate treatment often occurs from misdiagnosis as a chronic ankle sprain or a congenital flat foot. We report two cases of foot deformities caused by spontaneous and traumatic rupture of posterior tibial tendons with their clinical manifestations and MRI findings.