The possible causes of tendon pain behind the ankle are as follows: 1. Achilles tendonitis: the Achilles tendon is located at the back of the ankle joint. If you often perform strenuous sports activities or weight-bearing activities, such as hiking and climbing, going up and down stairs, it will cause the load on the Achilles tendon to increase for a long time, which will cause inflammation of the Achilles tendon, manifesting as pain in the Achilles tendon area. It may also be because the shoes worn are not suitable, such as wearing shoes too small, the heel of the shoe will be repeatedly rubbed with the Achilles tendon, over time will also appear Achilles tendon inflammation, manifested as pain in the tendon behind the ankle. 2, peroneal tendonitis: peroneal tendon is often in the tendon groove behind the ankle joint, around the ankle joint to the lateral side of the foot. If the peroneal tendon is rubbed, pain will also occur at the back of the outer ankle.