Ossification of the Achilles tendon is a rare condition that is characterized by the presence of an ossific mass contained within the substance of the tendon. The ossified mass is usually asymptomatic but when it grows large and painful, it deteriorates the function of Achilles tendon. We report a case of ossification of the Achilles tendon, which was successfully treated by removal of the ossific mass and proximal flexor hallucis longus (FHL) tendon transfer.