Damage to the tendon-ligamentous apparatus places serious limitations on a personʼs physical activity. Injuries are especially common in physically healthy people leading an active lifestyle, such as athletes. To treat such injuries in orthopaedics and traumatology, autoplastic operations are performed or prostheses made of synthetic or biological materials are installed. The known treatment methods, in spite of their effectiveness, have a number of serious drawbacks, which often limit their use. Therefore, the search for new approaches and materials for plastic ligaments is an urgent task. Today, biotissue prostheses are accumulating advantages over their synthetic counterparts. The most promising raw material for biological ligament prostheses, due to its availability in the required quantity and optimal size, is the flexor and extensor calf tendons. This paper aimed to develop a method for treating xenogenic tendon to manufacture ligament prostheses and assessing its biocompatibility in a heterotopic implantation model. To manufacture a ligament prosthesis, the raw material was subjected to mechanical cleaning and chemical-physical treatment, as well as treatment with supercritical carbon dioxide fluid with the addition of the nonionic surfactant Tween 80, which together contributed to effective decellularization and removal of other biologically active components, while maintaining the physical and mechanical parameters and natural fiberarchitectonics of native raw materials. The biocompatible properties of ligament prosthesis specimens made from the flexor and extensor calf tendons using this method were evaluated in a model of heterotopic implantation into the subcutaneous adipose tissue of rats. The results obtained confirm the promising use of this material, treated according to the proposed method, in clinical practice.