Abstract:[Objective] To observe regenerative capacity of the residual peroneus longus tendon secondary to anterior half tendon har- vested by magnetic resonance image. [Methods] A total of 19 patients had anterior half peroneus longus tendon harvested for single-bundle anterior cruciate ligament reconstruction. Magnetic resonance examinations were performed regularly before operation, the next day after op- eration, 1 month, 3 months, 1 year and 2 years after operation to obtain their magnetic resonance imaging data. The Dicom format images ob- tained were imported into RadiAnt DICOM Viewer software, and the tendon points were located using the software to obtain axial images at 2cm to the distal and proximal ends of the tendon harvested, and the cross- sectional area of the peroneus longus tendon was measured, Compared with the cross-sectional area of peroneus longus tendon at the same level before operation, its regeneration was analyzed. [Results] All the patients remained good continuity of the residual peroneus longus tendon without rupture on MRIs. At 3 months after opera- tion, the residual ligament harvested at the proximal end regenerated rapidly, up to 85% of the original cross sectional area, while which at the distal end was also thickened. At 1 year after operation, the proximal and distal ends of the tendon harvested were thickened significant- ly, exceeding the preoperative level, and basically recovered to the preoperative level at 2 years after operation. [Conclusion] The residual peroneus longus tendon has a strong regenerative capacity, therefor the anterior half of the tendon is suitable tendon autograft for clinical needs.